Data transmission method and apparatus

ABSTRACT

A method includes generating a preamble for a protocol version of a wireless local area network, where the preamble includes a legacy signal L-SIG field and a high efficiency signal HE-SIG field that are arranged in order, the HE-SIG field includes a first orthogonal frequency division multiplexing OFDM symbol and a second OFDM symbol that are arranged in order, and an input information bit of the first OFDM symbol is the same as that of the second OFDM symbol, and sending the preamble to a receive end device, so that the receive end device restores the preamble, and when determining that input information bits obtained after restoring the first OFDM symbol and the second OFDM symbol are the same, determines that the preamble is the preamble of the protocol version.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2015/080710, filed on Jun. 3, 2015, which claims priority toChinese Patent Application No. PCT/CN2014/088063, filed on Sep. 30, 2014and Chinese Patent Application No. PCT/CN2014/088661, filed on Oct. 15,2014. All of the aforementioned patent applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

Embodiments of the present invention relate to the field ofcommunications technologies, and more specifically, to a datatransmission method and an apparatus.

BACKGROUND

Standardization of a wireless local area network (WLAN) by using an802.11 standard family significantly reduces costs of a WLAN technology.Wireless Fidelity (Wi-Fi) is a brand of a wireless networkcommunications technology and held by the Wi-Fi Alliance, and anobjective of Wi-Fi is to improve interoperability between wirelessnetwork products based on the 802.11 standards. A wireless local areanetwork using a series of 802.11 protocols may be referred to as a Wi-Finetwork.

Currently, an 802.11 standard version has been evolved from 802.11a/b to802.11g, 802.11n, 802.11ac, and latest 802.11ax. To ensure backwardcompatibility and interoperability between products of different 802.11standard versions, a mixed format (MF) preamble (preamble for short) hasbeen defined since 802.11n. A legacy field part of the preamble is thesame as a preamble field of 802.11a, both including a legacy shorttraining field, a legacy long training field, and a legacy signal field.A preamble for a version later than 802.11n further includes, inaddition to a legacy field part, a non-legacy field part thatspecifically includes a non-legacy signal field, a non-legacy shorttraining field, a non-legacy long training field, and the like. Thenon-legacy field part of 802.11n is named as high throughput (HT, HighThroughput), that is, the non-legacy field part includes: a highthroughput signal field, a high throughput short training field, and ahigh throughput long training field. A non-legacy field part of 802.11acis named as very high throughput (VHT), that is, the non-legacy fieldpart includes: a very high throughput signal field A, a very highthroughput short training field, and a very high throughput longtraining field, and a very high throughput signal field B. In thecurrent 802.11 standard versions, distinction between protocol versionsand auto-detection at a receive end may be implemented according to amodulation manner of a symbol following a preamble legacy field.

For an 802.11ax version, how to use a preamble to distinguish betweenprotocol versions and implement rapid and reliable auto-detection of aprotocol version becomes a problem to be urgently resolved.

SUMMARY

Embodiments of the present invention provide a data transmission methodand an apparatus, so as to implement rapid and reliable auto-detectionof a preamble of an 802.11ax version.

According to a first aspect, a data transmission method is provided,including: generating a preamble for a protocol version of a wirelesslocal area network, where the preamble includes one or a combination ofa legacy signal L-SIG field and a high efficiency signal HE-SIG field,the L-SIG field or the HE-SIG field includes a first orthogonalfrequency division multiplexing OFDM symbol and a second OFDM symbolthat are arranged in order, and an input information bit of the firstOFDM symbol is the same as that of the second OFDM symbol, and sendingthe preamble to a receive end device.

According to a second aspect, a data transmission method is provided,including receiving a preamble sent by a transmit end device for aprotocol version of a wireless local area network, where the preambleincludes one or a combination of a legacy signal L-SIG field and a highefficiency signal HE-SIG field, the L-SIG field or the HE-SIG fieldincludes a first orthogonal frequency division multiplexing OFDM symboland a second OFDM symbol that are arranged in order, and an inputinformation bit of the second OFDM symbol is the same as that of thefirst OFDM symbol; restoring the first OFDM symbol and the second OFDMsymbol that are in the HE-SIG field of the preamble; determining thatsequences obtained after the first OFDM symbol and the second OFDMsymbol are restored are the same, that is, determining that the preambleis a preamble of the first protocol version; and processing a remainingfield of the preamble and a data part according to a predetermined ruleof the protocol version.

According to a third aspect, a transmit end device is provided,including: a generation unit, configured to generate a preamble for aprotocol version of a wireless local area network, where the preambleincludes one or a combination of a legacy signal L-SIG field and a highefficiency signal HE-SIG field, the L-SIG field or the HE-SIG fieldincludes a first orthogonal frequency division multiplexing OFDM symboland a second OFDM symbol that are arranged in order, and an inputinformation bit of the first OFDM symbol is the same as that of thesecond OFDM symbol; and a sending unit, configured to send the preambleto a receive end device.

According to a fourth aspect, a receive end device is provided,including: a receiving unit, configured to receive a preamble sent by atransmit end device for a protocol version of a wireless local areanetwork, where the preamble includes one or a combination of a legacysignal L-SIG field and a high efficiency signal HE-SIG field, the L-SIGfield or the HE-SIG field includes a first orthogonal frequency divisionmultiplexing OFDM symbol and a second OFDM symbol that are arranged inorder, and an input information bit of the second OFDM symbol is thesame as that of the first OFDM symbol; a restoration unit, configured torestore the first OFDM symbol and the second OFDM symbol that are in theHE-SIG field of the preamble; and a determining unit, configured todetermine that sequences obtained after the first OFDM symbol and thesecond OFDM symbol are restored are the same, that is, determining thatthe preamble is a preamble of the first protocol version; where therestoration unit is further configured to process a remaining field ofthe preamble and a data part according to a predetermined rule of theprotocol version.

According to the embodiments of the present invention, a preamble for aprotocol version of a wireless local area network is generated, wherethe preamble includes a legacy signal L-SIG field and a high efficiencysignal HE-SIG field that are arranged in order, the HE-SIG fieldincludes a first orthogonal frequency division multiplexing OFDM symboland a second OFDM symbol that are arranged in order, and an inputinformation bit of the first OFDM symbol is the same as that of thesecond OFDM symbol; and the preamble is sent to a receive end device, sothat the receive end device restores the preamble, and when determiningthat input information bits obtained after restoring the first OFDMsymbol and the second OFDM symbol are the same, determines that thepreamble is the preamble of the protocol version. Rapid and reliableauto-detection of a preamble of an 802.11ax protocol version can beimplemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection can be improved by using the first OFDM symbol and thesecond OFDM symbol that have the same input information bit.

BRIEF DESCRIPTION OF THE DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly describes the accompanyingdrawings required for describing the embodiments of the presentinvention. Apparently, the accompanying drawings in the followingdescription show merely some embodiments of the present invention, and aperson of ordinary skill in the art may still derive other drawings fromthese accompanying drawings without creative efforts.

FIG. 1 is a schematic structural diagram of a preamble according to anembodiment of the present invention;

FIG. 2 is a schematic flowchart of a data transmission method accordingto an embodiment of the present invention;

FIG. 3 is a schematic flowchart of a data transmission method accordingto an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a preamble according to anembodiment of the present invention;

FIG. 5 is a schematic structural diagram of a preamble according toanother embodiment of the present invention;

FIG. 6a and FIG. 6b are schematic structural diagrams of a preambleaccording to another embodiment of the present invention;

FIG. 7 is a schematic structural diagram of a preamble according toanother embodiment of the present invention;

FIG. 8 is a schematic block diagram of a transmit end device accordingto an embodiment of the present invention;

FIG. 9 is a schematic block diagram of a receive end device according toan embodiment of the present invention;

FIG. 10 is a structural block diagram of a transmit end device accordingto another embodiment of the present invention;

FIG. 11 is a structural block diagram of a receive end device accordingto another embodiment of the present invention;

FIG. 12 to FIG. 14 are schematic structural diagrams of a preambleaccording to some other embodiments of the present invention; and

FIG. 15 to FIG. 17 are schematic diagrams of operating principles ofsome other embodiments of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following clearly and completely describes the technical solutionsin the embodiments of the present invention with reference to theaccompanying drawings in the embodiments of the present invention.Apparently, the described embodiments are a part rather than all of theembodiments of the present invention. All other embodiments obtained bya person of ordinary skill in the art based on the embodiments of thepresent invention without creative efforts shall fall within theprotection scope of the present invention.

Technical solutions of the present invention may be applied to awireless local area network (WLAN) system, a Wireless Fidelity (Wi-Fi)system, and various other communications systems that need to use apreamble to notify a communications peer end of information such as adata rate and a data length of transmitted data.

Correspondingly, a transmit end device and a receive end device may be asubscriber station (STA) in a WLAN. The subscriber station may also bereferred to as a system, a subscriber unit, an access terminal, a mobilestation, a mobile console, a remote station, a remote terminal, a mobiledevice, a user terminal, a terminal, a wireless communications device, auser agent, a user apparatus, or UE (User Equipment, user equipment).The STA may be a cellular phone, a cordless phone, a SIP (SessionInitiation Protocol) phone, a WLL (wireless local loop) station, a PDA(personal digital assistant), a handheld device having a wireless localarea network (for example, Wi-Fi) communications function, a computingdevice, or another processing device connected to a wireless modem.

In addition, the transmit end device and the receive end device may beaccess points (Access Point) in a WLAN. The access point may be used tocommunicate with an access terminal by using the wireless local areanetwork, transmit data of the access terminal to a network side ortransmit data from a network side to the access terminal.

The receive end device may be a communications peer end corresponding tothe transmit end device.

For ease of understanding and description, as an example but notlimitation, the following describes execution processes and actions ofthe data transmission method and the apparatus of the present inventionin a Wi-Fi system.

FIG. 1 is a structural diagram of a preamble according to an embodimentof the present invention.

As shown in FIG. 1, a legacy part of the preamble includes three fields:a legacy short training field (L-SIF) field, a legacy long trainingfield (L-LTF) field, and a legacy signal (L-SIG) field. The L-STF fieldis used in start-of-frame detection, an auto gain control (AGC) setting,initial frequency offset estimation, and initial time synchronization.The L-LTF is used in more accurate frequency offset estimation and timesynchronization, and is also used to generate channel estimation forreceiving and equalizing an L-SIG. The L-SIG field is mainly used tocarry data rate information and data length information, so that thereceive end device can determine, according to the data rate informationand data length information, a length of data that is carried in a sameframe with the preamble, and further determine proper idle time.

For an 802.11ax preamble, a non-legacy field of the preamble may benamed as a high efficiency wireless local area network (HEW, HighEfficiency WLAN) or high efficiency (HE, High Efficiency), that is, anon-legacy field part includes: a high efficiency wireless local areanetwork signal (HEW-SIG) field, a high efficiency wireless local areanetwork short training (HEW-STF) field, and a high efficiency wirelesslocal area network long training (HEW-LTF) field; or a high efficiencysignal (HE-SIG) field, a high efficiency short training (HE-STF) field,and a high efficiency long training (HE-LTF) field. Naming of thenon-legacy field of the 802.11ax preamble is not limited in the presentinvention, and for ease of description, the following embodiments mainlyuse the HE-SIG as an example for description.

As shown in FIG. 1, the L-SIG field in the legacy part of the preambleis followed by the HE-SIG field in the non-legacy part. The HE-SIG fieldmay include at least two parts. A first part follows the L-SIG andincludes at least two OFDM symbols, and a second part may follow theHE-STF and the HE-LTF. The HE-SIG field is used to carry signalinginformation in an 802.11ax version protocol, and can be used inidentification and auto-detection of the 802.11ax preamble and a datapacket.

FIG. 2 is a schematic flowchart of a data transmission method accordingto an embodiment of the present invention. The method in FIG. 2 may beexecuted by a transmit end device, and the transmit end device may be anaccess point AP, a station STA, or the like in a wireless local areanetwork.

201. Generate a preamble for a protocol version of the wireless localarea network, where the preamble includes a legacy signal L-SIG fieldand a high efficiency signal HE-SIG field that are arranged in order,the HE-SIG field includes a first orthogonal frequency divisionmultiplexing OFDM symbol and a second OFDM symbol that are arranged inorder, and an input information bit of the first OFDM symbol is the sameas that of the second OFDM symbol.

202. Send the preamble to a receive end device, so that the receive enddevice restores the preamble, and when determining that inputinformation bits obtained after restoring the first OFDM symbol and thesecond OFDM symbol are the same, determines that the preamble is thepreamble of the protocol version.

When generating a preamble for a protocol version of a wireless localarea network, the transmit end device in this embodiment of the presentinvention generates a first orthogonal frequency division multiplexingOFDM symbol and a second OFDM symbol according to a same inputinformation bit, and input information bits obtained after a receive enddevice restores the first OFDM symbol and the second OFDM symbol can bethe same, so that the receive end device determines that the preamble isthe preamble of the protocol version, and rapid and reliableauto-detection of a preamble of an 802.11ax version can be implemented.In addition, when 802.11ax is applied to an outdoor scenario,reliability and correctness of preamble transmission and auto-detectionmay be improved by using the first OFDM symbol and the second OFDMsymbol that include a same bit sequence.

First, a transmit end device supporting a protocol version of thewireless local area network generates a to-be-transmitted preamble ofthe protocol version. Specifically, the transmit end device determinesan original information bit that needs to be carried in each field ofthe preamble, and performs processing such as channel coding,interleaving, and modulation on the original information bit, so as togenerate a preamble including multiple OFDM symbols. The followingembodiment mainly describes a generation process of an HE-SIG field thatfollows a legacy signal field L-SIG field in the preamble of theprotocol version. A generation process of a legacy part (an L-STF field,an L-LTF field, and the L-SIG field) of the preamble may be the same asthat in an existing older version protocol (such as 802.11a/n/ac).

It should be understood that the HE-SIG field includes at least twoparts. A first part immediately follows the L-SIG field, and a secondpart may be in any location of a non-legacy part. In a preferredembodiment, the second part may follow the HE-STF and the HE-LTF. Thisembodiment of the present invention mainly targets the first part of theHE-SIG field.

It should also be understood that this embodiment of the presentinvention does not limit a naming manner of the HE-SIG field, which maybe high efficiency (HE, High Efficiency), a high efficiency wirelesslocal area network (HEW, High Efficiency WLAN), or the like.

Optionally, in an embodiment, the generating a preamble for a protocolversion of a wireless local area network includes: processing the inputinformation bit by using a channel encoder, a first interleaver, and afirst modulator to generate the first OFDM symbol; and processing theinput information bit by using the channel encoder, a secondinterleaver, and a second modulator to generate the second OFDM symbol,where the first interleaver and the second interleaver are different,and the first modulator and the second modulator are the same ordifferent.

When generating the HE-SIG field, the transmit end device may firstdetermine an initial bit sequence according to signaling informationthat needs to be carried in the HE-SIG field, then generates an inputinformation bit by sequentially capturing a bit sequence from theinitial bit sequence according to a quantity of bits that can be carriedin one OFDM symbol, and then processes the input information bit togenerate the first OFDM symbol and the second OFDM symbol.

Specifically, the input information bit may be scrambled first, channelcoding is performed by using the channel encoder, a sequence obtainedafter channel coding is interleaved by using the first interleaver andmodulated by using the first modulator in a first modulation manner, andoperations such as spatial flow shift, transformation to the timedomain, and guard interval addition are performed, so as to generate thefirst OFDM symbol.

Similarly, the input information bit may be scrambled first, channelcoding is performed by using the channel encoder, a sequence obtainedafter channel coding is interleaved by using the second interleaver andmodulated by using the second modulator in a second modulation manner,and operations such as spatial flow shift, transformation to the timedomain, and guard interval addition are performed, so as to generate thesecond OFDM symbol.

Both generation processes of the first OFDM symbol and the second OFDMsymbol include interleaving processing, but the first interleaver andthe second interleaver that perform interleaving processing aredifferent. In addition, modulation manners of the first OFDM symbol andthe second OFDM symbol may be the same or different, that is, the firstmodulator and the second modulator may be the same or different. In apreferred example, the modulation manner of the first OFDM symbol may beBPSK, and the modulation manner of the second OFDM symbol may also beBPSK; or the modulation manner of the first OFDM symbol is BPSK, and themodulation manner of the second OFDM symbol is QBPSK.

Optionally, in an embodiment, the generating a preamble for a protocolversion of a wireless local area network includes: processing the inputinformation bit by using a channel encoder, an interleaver, and a firstmodulator to generate the first OFDM symbol; and processing the inputinformation bit by using the channel encoder and a second modulator togenerate the second OFDM symbol, where the first modulator and thesecond modulator are the same or different. Specifically, a generationprocess of the first OFDM symbol may include interleaving processing,and a generation process of the second OFDM symbol may not includeinterleaving processing. Other processing processes are similar to thosein the foregoing embodiment, and details are not described herein again.

Optionally, in an embodiment, the generating a preamble for a protocolversion of a wireless local area network includes: processing the inputinformation bit by using a channel encoder and a first modulator togenerate the first OFDM symbol; and processing the input information bitby using the channel encoder, an interleaver, and a second modulator togenerate the second OFDM symbol, where the first modulator and thesecond modulator are the same or different. Specifically, a generationprocess of the first OFDM symbol may not include interleavingprocessing, and a generation process of the second OFDM symbol mayinclude interleaving processing. Other processing processes are similarto those in the foregoing embodiment, and details are not describedherein again.

Optionally, in an embodiment, the generating a preamble for a protocolversion of a wireless local area network includes: processing the inputinformation bit by using a channel encoder and a first modulator togenerate the first OFDM symbol; and processing the input information bitby using the channel encoder and a second modulator to generate thesecond OFDM symbol, where the first modulator and the second modulatorare the same or different. Specifically, neither generation processes ofthe first OFDM symbol and the second OFDM symbol may includeinterleaving processing. Other processing processes are similar to thosein the foregoing embodiment, and details are not described herein again.

Optionally, in an embodiment, the generating a preamble for a protocolversion of a wireless local area network includes: processing the inputinformation bit by using a channel encoder, an interleaver, and a firstmodulator to generate the first OFDM symbol; and processing the inputinformation bit by using the channel encoder, an interleaver, and asecond modulator to generate the second OFDM symbol, where the firstmodulator and the second modulator are the same or different. The firstOFDM symbol and the second OFDM symbol pass a same interleaver. Otherprocessing processes are similar to those in the foregoing embodiment,and details are not described herein again.

Optionally, in an embodiment, a subcarrier spacing used by the firstOFDM symbol and the second OFDM symbol is 312.5 kHz, and a guardinterval GI between the first OFDM symbol and the second OFDM symbol is0.8 μs. It should be understood that, to ensure compatibility with anexisting protocol version and unaffected performance of a receive end ofthe existing protocol version, an OFDM symbol in the HE-SIG field of thepreamble may use a subcarrier spacing and a guard interval that are thesame as those in the legacy field part.

Optionally, in an embodiment, a third OFDM symbol that follows thesecond OFDM symbol is generated, where an input information bit of thethird OFDM symbol includes a part or all of information bits, except theinput information bit of the first OFDM symbol or the second OFDMsymbol, in information bits that need to be carried in the HE-SIG field,a subcarrier spacing used by the third symbol is 312.5 kHz, and a guardinterval GI for the third OFDM symbol is 1.6 μs or 2.4 μs.

When the input information bit of the first OFDM symbol and the secondOFDM symbol includes only a part of the information bits that need to becarried in the HE-SIG field, the part or all of the information bits,except the input information bit of the first OFDM symbol or the secondOFDM symbol, in the information bits that need to be carried in theHE-SIG field may be carried in the third OFDM symbol.

That is, after the second OFDM symbol, the third OFDM symbol may begenerated. Specifically, the input information bit of the third OFDMsymbol may be scrambled first, channel coding is performed by using thechannel encoder, a sequence obtained after channel coding isinterleaved, by using the same first interleaver used by the first OFDMsymbol, and modulated, and operations such as spatial flow shift,transformation to the time domain, and guard interval addition areperformed, so as to generate the third OFDM symbol. Preferably, amodulation manner of the third OFDM symbol may be BPSK or QBPSK. Theinterleaving manner of the third OFDM symbol may be the same as ordifferent from that of the first OFDM symbol, or may be the same as ordifferent from that of the second OFDM symbol. The guard interval of thethird OFDM symbol may be determined according to a protocol version ofthe foregoing preamble, that is, an 802.11ax protocol version maypredefine a symbol that follows the first OFDM symbol and the secondOFDM symbol, a field, and a guard interval of a data part. Preferably,the guard interval for the third OFDM symbol may be 1.6 μs or 2.4 μs.

Optionally, in an embodiment, the method further includes: generating athird OFDM symbol that follows the second OFDM symbol, where an inputinformation bit of the third OFDM symbol includes a part or all ofinformation bits, except the input information bit of the first OFDMsymbol or the second OFDM symbol, in information bits that need to becarried in the HE-SIG field; and generating a fourth OFDM symbol thatfollows the third OFDM symbol, where an input information bit of thefourth OFDM symbol is the same as the input information bit of the thirdOFDM symbol, a subcarrier spacing used by the third OFDM symbol and thefourth OFDM symbol is 312.5 kHz, and a guard interval GI between thethird OFDM symbol and the fourth OFDM symbol is 0.8 μs.

When the input information bit of the first OFDM symbol and the secondOFDM symbol includes only a part of the information bits that need to becarried in the HE-SIG field, the part or all of the information bits,except the input information bit of the first OFDM symbol or the secondOFDM symbol, in the information bits that need to be carried in theHE-SIG field may be carried in the third OFDM symbol and the fourth OFDMsymbol. Generation processes of the third OFDM symbol and the fourthOFDM symbol may be similar to the generation processes of the first OFDMsymbol and the second OFDM symbol, and details are not described herein.Preferably, interleaving and modulation manners of the third OFDM symbolare the same as those of the first OFDM symbol, and interleaving andmodulation manners of the fourth OFDM symbol are the same as those ofthe second OFDM symbol.

When generating a preamble for a protocol version of a wireless localarea network, the transmit end device in this embodiment of the presentinvention generates a first orthogonal frequency division multiplexingOFDM symbol and a second OFDM symbol according to a same inputinformation bit, and input information bits obtained after a receive enddevice restores the first OFDM symbol and the second OFDM symbol can bethe same, so that the receive end device determines that the preamble isthe preamble of the protocol version, and rapid and reliableauto-detection of a preamble of an 802.11ax version can be implemented.In addition, when 802.11ax is applied to an outdoor scenario,reliability and correctness of preamble transmission and auto-detectionmay be improved by using the first OFDM symbol and the second OFDMsymbol that include a same bit sequence. In addition, a subcarrierspacing and a guard interval that are used by the first OFDM symbol andthe second OFDM symbol are the same as a subcarrier spacing and a guardinterval used in an existing protocol version. Therefore, normalreception of an 802.11ax preamble at a receive end of the existingprotocol version can be ensured, not affecting performance of thereceive end of the existing protocol version.

FIG. 3 is a schematic flowchart of a data transmission method accordingto an embodiment of the present invention. The method in FIG. 3 may beexecuted by a receive end device, and the receive end device may be anaccess point AP, a station STA, or the like in a wireless local areanetwork.

301. Receive a preamble sent by a transmit end device for a protocolversion of the wireless local area network, where the preamble includesa legacy signal L-SIG field and a high efficiency signal HE-SIG fieldthat are arranged in order, the HE-SIG field includes a first orthogonalfrequency division multiplexing OFDM symbol and a second OFDM symbolthat are arranged in order, and an input information bit of the secondOFDM symbol is the same as that of the first OFDM symbol.

302. Restore the first OFDM symbol and the second OFDM symbol that arein the HE-SIG field of the preamble.

303. Determine that sequences obtained after the first OFDM symbol andthe second OFDM symbol are restored are the same, that is, determinethat the preamble is a preamble of a first protocol version.

304. Process a remaining field of the preamble and a data part accordingto a predetermined rule of the protocol version.

The receive end device in this embodiment of the present inventionreceives a preamble sent by a transmit end device for a protocol versionof a wireless local area network, restores a first OFDM symbol and asecond OFDM symbol that are in an HE-SIG field of the preamble, and whendetermining that input information bits obtained after restoring thefirst OFDM symbol and the second OFDM symbol are the same, determinesthat the preamble is a preamble of a first protocol version. Rapid andreliable auto-detection of a preamble of an 802.11ax version can beimplemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection may be improved by using the first OFDM symbol and thesecond OFDM symbol that include a same bit sequence.

First, a transmit end device supporting a protocol version of thewireless local area network generates a to-be-transmitted preamble ofthe protocol version. Specifically, the transmit end device determinesan original information bit that needs to be carried in each field ofthe preamble, and performs processing such as channel coding,interleaving, and modulation on the original information bit, so as togenerate a preamble including multiple OFDM symbols. The followingembodiment mainly describes a restoration process of an HE-SIG fieldthat follows a legacy signal field L-SIG field in the preamble of theprotocol version.

It should be understood that the HE-SIG field includes at least twoparts. A first part immediately follows the L-SIG field, and a secondpart may be in any location of a non-legacy part. In a preferredembodiment, the second part may follow an HE-STF and an HE-LTF. Thisembodiment of the present invention mainly targets the first part of theHE-SIG field.

It should also be understood that this embodiment of the presentinvention does not limit a naming manner of the HE-SIG field, which maybe high efficiency (HE, High Efficiency), high efficiency wireless localarea network (HEW, High Efficiency WLAN), or the like.

Optionally, in an embodiment, the restoring the first OFDM symbol andthe second OFDM symbol that are in the HE-SIG field of the preambleincludes: processing the first OFDM symbol by using a firstde-interleaver to generate a first sequence; and processing the secondOFDM symbol by using a second de-interleaver to generate a secondsequence, so as to determine that the first sequence is the same as thesecond sequence, that is, to determine that the preamble is the preambleof the first protocol version, where the first de-interleaver and thesecond de-interleaver are different.

When generating the HE-SIG field of the preamble, the transmit enddevice generates the first OFDM symbol and the second OFDM symbolaccording to a same input bit sequence. A process in which the receiveend restores the first OFDM symbol and the second OFDM symbol may beconsidered as an inverse process of a generation process performed bythe transmit end device, that is, demodulation, de-interleaving, anddecoding that are performed on the first OFDM symbol and the second OFDMsymbol by the receive end device are corresponding to modulation,interleaving, and encoding that are performed on the first OFDM symboland the second OFDM symbol by the transmit end device. Specifically, thetransmit end device generates the first OFDM symbol by using an encoder,a first modulator, and a first interleaver. A modulation mannercorresponding to the first modulator may be BPSK. Correspondingly, whenrestoring the first OFDM symbol, the receive end device needs tode-interleave the first OFDM symbol by using a first de-interleavercorresponding to the first interleaver. The transmit end devicegenerates the second OFDM symbol by using the same encoder and firstmodulator that are used for the first OFDM symbol, and by using a secondinterleaver that is different from the first interleaver used for thefirst OFDM symbol. Correspondingly, when restoring the second OFDMsymbol, the receive end device needs to de-interleave the first OFDMsymbol by using a second de-interleaver corresponding to the secondinterleaver. Then the de-interleaved first OFDM symbol is compared withthe de-interleaved second OFDM symbol, and if sequences are the same,the preamble may be determined as an 802.11ax preamble.

Optionally, in an embodiment, the restoring the first OFDM symbol andthe second OFDM symbol that are in the HE-SIG field of the preambleincludes: processing the first OFDM symbol by using a first demodulatorand a de-interleaver to generate a first sequence; and processing thesecond OFDM symbol by using a second demodulator to generate a secondsequence, so as to determine that the first sequence is the same as thesecond sequence, that is, to determine that the preamble is the preambleof the first protocol version, where the first demodulator and thesecond demodulator are the same or different.

Specifically, the transmit end device generates the first OFDM symbol byusing an encoder, a first modulator, and an interleaver. A modulationmanner corresponding to the first modulator may be BPSK.Correspondingly, when restoring the first OFDM symbol, the receive enddevice needs to de-interleave the first OFDM symbol by using ade-interleaver corresponding to the interleaver. The transmit end devicegenerates the second OFDM symbol by using the same encoder and secondmodulator that are used to generate the first OFDM symbol, andinterleaving is not performed. A modulation manner corresponding to thesecond modulator may be QBPSK. Correspondingly, when restoring thesecond OFDM symbol, the receive end device needs to rotate the OFDMsymbol 90 degrees clockwise by using the second demodulator. Then thede-interleaved first OFDM symbol is compared with the de-interleavedsecond OFDM symbol, and if sequences are the same, the preamble may bedetermined as an 802.11ax preamble.

Optionally, in an embodiment, the restoring the first OFDM symbol andthe second OFDM symbol that are in the HE-SIG field of the preambleincludes: processing the first OFDM symbol by using a first demodulatorto generate a first sequence; and processing the second OFDM symbol byusing a second demodulator and a de-interleaver to generate a secondsequence, so as to determine that the first sequence is the same as thesecond sequence, that is, to determine that the preamble is the preambleof the first protocol version, where the first demodulator and thesecond demodulator are the same or different.

Specifically, the transmit end device generates the first OFDM symbol byusing an encoder and a first modulator, and interleaving is notperformed. A modulation manner corresponding to the first modulator maybe BPSK. The transmit end device generates the second OFDM symbol byusing an encoder, a second modulator, and an interleaver. A modulationmanner corresponding to the second modulator may be QBPSK.Correspondingly, when restoring the second OFDM symbol, the receive enddevice needs to de-interleave the second OFDM symbol by using ade-interleaver corresponding to the interleaver and perform phaserotation on the second OFDM symbol by 90 degrees clockwise by using thesecond demodulator. Then the processed first OFDM symbol is comparedwith the de-interleaved and demodulated second OFDM symbol, and ifsequences are the same, the preamble may be determined as an 802.11axpreamble.

Optionally, in an embodiment, the restoring the first OFDM symbol andthe second OFDM symbol that are in the HE-SIG field of the preambleincludes: processing the first OFDM symbol by using a first demodulatorto generate a first sequence; and processing the second OFDM symbol byusing a second demodulator to generate a second sequence, so as todetermine that the first sequence is the same as the second sequence,that is, to determine that the preamble is the preamble of the firstprotocol version, where the first demodulator and the second demodulatorare the same or different.

Optionally, in an embodiment, the restoring the first OFDM symbol andthe second OFDM symbol that are in the HE-SIG field of the preambleincludes: processing the first OFDM symbol by using a de-interleaver togenerate a first sequence; and processing the second OFDM symbol byusing the de-interleaver to generate a second sequence, so as todetermine that the first sequence is the same as the second sequence,that is, to determine that the preamble is the preamble of the firstprotocol version.

Optionally, in an embodiment, a subcarrier spacing used by the firstOFDM symbol and the second OFDM symbol is 312.5 kHz, and a guardinterval GI between the first OFDM symbol and the second OFDM symbol is0.8 μs.

The receive end device in this embodiment of the present inventionreceives a preamble sent by a transmit end device for a protocol versionof a wireless local area network, restores a first OFDM symbol and asecond OFDM symbol that are in an HE-SIG field of the preamble, and whendetermining that input information bits obtained after restoring thefirst OFDM symbol and the second OFDM symbol are the same, determinesthat the preamble is a preamble of a first protocol version. Rapid andreliable auto-detection of a preamble of an 802.11ax version can beimplemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection may be improved by using the first OFDM symbol and thesecond OFDM symbol that include a same bit sequence. In addition, asubcarrier spacing and a guard interval that are used by the first OFDMsymbol and the second OFDM symbol are the same as a subcarrier spacingand a guard interval used in an existing protocol version. Therefore,normal reception of an 802.11ax preamble at a receive end of theexisting protocol version can be ensured, not affecting performance ofthe receive end of the existing protocol version.

FIG. 4 is a schematic structural diagram of a preamble according to anembodiment of the present invention.

In a preferred embodiment, an 802.11ax transmit end may generate thepreamble shown in FIG. 4. A legacy part of the preamble includes threefields: an L-STF, an L-LTF, and an L-SIG, and the three fields of thelegacy part occupy 20 μs in total. A first part of an HE-SIG fieldfollows the L-SIG field and is denoted as HE-SIGs, and a second partfollowing an HE-LTF or in any other location of the HE-SIG field isdenoted as HE-SIG2. An HE-SIG1 part includes two OFDM symbols: a firstOFDM symbol and a second OFDM symbol. It should be understood that whenthe first part of the HE-SIG field includes at least two OFDM symbols,the first two OFDM symbols may be denoted as HE-SIG0, a remaining symbolexcept the first two OFDM symbols in the first part may be denoted asHE-SIGs, and the second part of the HE-SIG field may be denoted asHE-SIG2.

The first OFDM symbol uses a subcarrier spacing of 312.5 kHz and a guardinterval of 0.8 μs. An input information bit carried in the first OFDMsymbol goes through a channel encoder and a first interleaver, and ismodulated by using BPSK.

The second OFDM symbol also uses the subcarrier spacing of 312.5 kHz andthe guard interval of 0.8 μs. An input information bit of the secondOFDM symbol is the same as that of the first OFDM symbol, and isprocessed by using the channel encoder and a second interleaver and thenmodulated by using the BPSK.

A subsequent OFDM symbol (including a remaining field of the preambleand a data part) following the second OFDM symbol may use a subcarrierspacing of 312.5 kHz or another value and a guard interval of 0.8 μs oranother value according to a rule of 802.11ax.

After receiving the foregoing preamble, a receive end device may performchannel equalization on the first OFDM symbol and the second OFDM symbolthat follow the L-SIG field, so as to obtain a first frequency domainsequence and a second frequency domain sequence, respectively, and cachethe first frequency domain sequence and the second frequency domainsequence for subsequent processing. Then the first frequency domainsequence is de-interleaved by using a first (de-)interleaver to obtain athird frequency domain sequence, and the second frequency domainsequence is de-interleaved by using a second (de-)interleaver to obtaina fourth frequency domain sequence. Then it is determined throughcomparison whether information carried in a subcarrier corresponding tothe third frequency domain sequence is the same as information carriedin a subcarrier corresponding to the fourth frequency domain sequence.If the information is the same, the preamble is determined as an802.11ax preamble, and subsequent data is determined as a data packet of802.11ax. If the information is not the same, a protocol version of thepreamble is identified by using an existing method for automaticallydetecting a protocol version.

When an 802.11n/ac receive end receives the foregoing 802.11ax preamble,because both the two OFDM symbols following the L-SIG field aremodulated by using the BPSK, the 802.11n/ac receive end identifies apreamble and data of 802.11ax as a preamble and data of 802.11a, therebynot affecting performance and compatibility of the 802.11n/ac receiveend.

Rapid and reliable auto-detection of a preamble of an 802.11ax versioncan be implemented by an 802.11ax receive end by using the methodaccording to the embodiments of the present invention. In addition, when802.11ax is applied to an outdoor scenario, reliability and correctnessof preamble transmission and auto-detection may be improved by using thefirst OFDM symbol and the second OFDM symbol that include a same inputinformation bit. In addition, a subcarrier spacing and a guard intervalthat are used by the first OFDM symbol and the second OFDM symbol arethe same as a subcarrier spacing and a guard interval used in anexisting protocol version, and both the first OFDM symbol and the secondOFDM symbol are modulated by using BPSK. Therefore, normal reception ofan 802.11ax preamble at a receive end of the existing protocol versioncan be ensured, not affecting performance of the receive end of theexisting protocol version.

FIG. 5 is a schematic structural diagram of a preamble according toanother embodiment of the present invention.

An 802.11ax transmit end may generate the preamble shown in FIG. 5. Afirst part of an HE-SIG field follows the L-SIG field and is denoted asHE-SIGs, and a second part of the HE-SIG field follows an HE-STF and anHE-LTF and is denoted as HE-SIG2. An HE-SIGs part includes two OFDMsymbols: a first OFDM symbol and a second OFDM symbol. It should beunderstood that when the first part of the HE-SIG field includes atleast two OFDM symbols, the first two OFDM symbols may be denoted asHE-SIG0, a remaining symbol except the first two OFDM symbols in thefirst part may be denoted as HE-SIGs, and the second part of the HE-SIGfield may be denoted as HE-SIG2.

The first OFDM symbol uses a subcarrier spacing of 312.5 kHz and a guardinterval of 0.8 μs. An input information bit carried in the first OFDMsymbol goes through a channel encoder and a first interleaver, and ismodulated by using BPSK.

The second OFDM symbol also uses the subcarrier spacing of 312.5 kHz andthe guard interval of 0.8 μs. An input information bit of the secondOFDM symbol is the same as that of the first OFDM symbol, and isprocessed by using the channel encoder and then modulated by using QBPSKwithout being interleaved.

A subsequent OFDM symbol (including a remaining field of the preambleand a data part) following the second OFDM symbol may use a subcarrierspacing of 312.5 kHz or another value and a guard interval of 0.8 μs oranother value according to a rule of 802.11ax.

After receiving the foregoing preamble, a receive end device may performchannel equalization on the first OFDM symbol and the second OFDM symbolthat follow the L-SIG field, so as to obtain a first frequency domainsequence and a second frequency domain sequence, respectively, and cachethe first frequency domain sequence and the second frequency domainsequence for subsequent processing. Then the first frequency domainsequence is de-interleaved by using a first (de-)interleaver to obtain athird frequency domain sequence. A modulation manner of the second OFDMsymbol is QBPSK, and as shown in the lower part of FIG. 5, constellationmapping in QBPSK modulation is phase-rotated by 90 degreescounterclockwise relative to that in BPSK modulation. Therefore, whenrestoring the second OFDM symbol, the receive end needs to perform phaserotation on the foregoing second frequency domain sequence by 90 degreesclockwise to obtain a fourth frequency domain sequence.

Then it is determined through comparison whether information carried ina subcarrier corresponding to the third frequency domain sequence is thesame as information carried in a subcarrier corresponding to the fourthfrequency domain sequence. If the information is the same, the preambleis determined as an 802.11ax preamble, and subsequent data is determinedas a data packet of 802.11ax. If the information is not the same, aprotocol version of the preamble is identified by using an existingmethod for automatically detecting a protocol version. The subsequentOFDM symbol (including a remaining part of the preamble and a data part)may be processed according to a rule of an 802.11ax protocol, and asubcarrier spacing and a guard interval that are corresponding to thetransmit end.

When an 802.11n receive end receives the foregoing 802.11ax preamble,because a first OFDM symbol that follows the L-SIG field is modulated byusing the BPSK, the 802.11n receive end identifies the 802.11ax preambleas an 802.11a preamble and processes the 802.11ax preamble in a mannerof processing the 802.11a preamble, thereby not affecting performanceand compatibility of the receive end.

When an 802.11ac receive end receives the foregoing 802.11ax preamble,because the first OFDM symbol that follows the L-SIG field is modulatedby using the BPSK and a second OFDM symbol is modulated by using theQBPSK, the 802.11ac receive end identifies the 802.11ax preamble as an802.11ac preamble and processes the 802.11ax preamble in a manner ofprocessing the 802.11ac preamble. A CRC verification failure is causedby decoding the HE-SIG field by the 802.11ac receive end in a manner ofdecoding a VHT-SIG field. Therefore, backoff is performed according to adata length indicated in the L-SIG field, not affecting performance andcompatibility of the 802.11ac receive end.

FIG. 6a and FIG. 6b are schematic structural diagrams of a preambleaccording to another embodiment of the present invention.

In an embodiment, an 802.11ax transmit end can generate the preamblesshown in FIG. 6a and FIG. 6b . A legacy part of the preamble includesthree fields: an L-STF, an L-LTF, and an L-SIG, and the three fields ofthe legacy part occupy 20 μs in total. A first part of an HE-SIG fieldfollows the L-SIG field and is denoted as HE-SIGs, and a second part ofthe HE-SIG field follows an HE-STF and an HE-LTF and is denoted asHE-SIG2. It should be understood that when the first part of the HE-SIGfield includes at least two OFDM symbols, the first two OFDM symbols maybe denoted as HE-SIG0, a remaining symbol except the first two OFDMsymbols in the first part may be denoted as HE-SIGs, and the second partof the HE-SIG field may be denoted as HE-SIG2.

As shown in FIG. 6a and FIG. 6b , the first part of the HE-SIG fieldincludes three OFDM symbols. A first OFDM symbol uses a subcarrierspacing of 312.5 kHz and a guard interval of 0.8 μs. An inputinformation bit carried in the first OFDM symbol goes through a channelencoder and a first interleaver, and is modulated by using BPSK. Asecond OFDM symbol also uses the subcarrier spacing of 312.5 kHz and theguard interval of 0.8 μs. An input information bit of the second OFDMsymbol is the same as that of the first OFDM symbol, and is processed byusing the channel encoder and a second interleaver and then modulated byusing the BPSK.

A third OFDM symbol may use a subcarrier spacing of 312.5 kHz or anothervalue and a guard interval of 0.8 μs or another value. For example, theguard interval of the third OFDM symbol shown in FIG. 6b is implementedby using different cyclic prefixes. A grey signal in the figure is acyclic prefix, and lengths of cyclic prefixes of the first OFDM symboland the second OFDM symbol are different from a length of a cyclicprefix of the third OFDM symbol. An input information bit of the thirdOFDM symbol is different from the input information bit of the firstOFDM symbol and the second OFDM symbol, and is a part or all of bitsequences, except the input information bit of the first OFDM symbol andthe second OFDM symbol, in original information bits that need to becarried in the HE-SIG field.

An input bit sequence of the third OFDM symbol is processed by using thechannel encoder and the first interleaver and modulated by using theBPSK.

After receiving the foregoing preamble, a receive end device may performchannel equalization on the first OFDM symbol and the second OFDM symbolthat follow the L-SIG field, so as to obtain a first frequency domainsequence and a second frequency domain sequence, respectively, and cachethe first frequency domain sequence and the second frequency domainsequence for subsequent processing. Then the first frequency domainsequence is de-interleaved by using a first (de-)interleaver to obtain athird frequency domain sequence, and the second frequency domainsequence is de-interleaved by using a second (de-)interleaver to obtaina fourth frequency domain sequence. Then it is determined throughcomparison whether information carried in a subcarrier corresponding tothe third frequency domain sequence is the same as information carriedin a subcarrier corresponding to the fourth frequency domain sequence.If the information is the same, the preamble is determined as an802.11ax preamble, and subsequent data is determined as a data packet of802.11ax. If the information is not the same, a protocol version of thepreamble is identified by using an existing method for automaticallydetecting a protocol version.

When an 802.11n/ac receive end receives the foregoing 802.11ax preamble,because both the two OFDM symbols following the L-SIG field aremodulated by using the BPSK, the 802.11n/ac receive end identifies apreamble and data of 802.11ax as a preamble and data of 802.11a, notaffecting performance and compatibility of the 802.11n/ac receive end aswell.

FIG. 7 is a schematic structural diagram of a preamble according toanother embodiment of the present invention.

An 802.11ax transmit end may generate the preamble shown in FIG. 7. Alegacy part of the preamble includes three fields: an L-STF, an L-LTF,and an L-SIG, and the three fields of the legacy part occupy 20 μs intotal. A first part of an HE-SIG field follows the L-SIG field and isdenoted as HE-SIGs, and a second part of the HE-SIG field follows anHE-STF and an HE-LTF and is denoted as HE-SIG2. It should be understoodthat when the first part of the HE-SIG field includes at least two OFDMsymbols, the first two OFDM symbols may be denoted as HE-SIG0, aremaining symbol except the first two OFDM symbols in the first part maybe denoted as HE-SIG1, and the second part of the HE-SIG field may bedenoted as HE-SIG2.

As shown in FIG. 7, a first OFDM symbol in the HE-SIG field uses asubcarrier spacing of 312.5 kHz and a guard interval of 0.8 μs. An inputinformation bit carried in the first OFDM symbol goes through a channelencoder and a first interleaver, and is modulated by using BPSK. Asecond OFDM symbol also uses the subcarrier spacing of 312.5 kHz and theguard interval of 0.8 μs. An input information bit of the second OFDMsymbol is the same as that of the first OFDM symbol, and is processed byusing the channel encoder and a second interleaver and then modulated byusing the BPSK.

A third OFDM symbol uses the subcarrier spacing of 312.5 kHz and theguard interval of 0.8 μs. An input information bit carried in the thirdOFDM symbol is processed by using the channel encoder and the firstinterleaver and modulated by using the BPSK. A fourth OFDM symbol alsouses the subcarrier spacing of 312.5 kHz and the guard interval of 0.8μs. An input information bit of the fourth OFDM symbol is the same asthat of the third OFDM symbol, and is processed by using the channelencoder and the second interleaver and then modulated by using the BPSK.The input information bit of the third OFDM symbol and the fourth OFDMsymbol is different from the input information bit of the first OFDMsymbol and the second OFDM symbol.

Another symbol (including a remaining field of the preamble and a datapart) following the fourth OFDM symbol may use a subcarrier spacing of312.5 kHz or another value and a guard interval of 0.8 μs or anothervalue.

After receiving the foregoing preamble, a receive end device may performchannel equalization on the first OFDM symbol and the second OFDM symbolthat follow the L-SIG field, so as to obtain a first frequency domainsequence and a second frequency domain sequence, respectively, and cachethe first frequency domain sequence and the second frequency domainsequence for subsequent processing. Then the first frequency domainsequence is de-interleaved by using a first (de-)interleaver to obtain athird frequency domain sequence, and the second frequency domainsequence is de-interleaved by using a second (de-)interleaver to obtaina fourth frequency domain sequence. Then it is determined throughcomparison whether information carried in a subcarrier corresponding tothe third frequency domain sequence is the same as information carriedin a subcarrier corresponding to the fourth frequency domain sequence.If the information is the same, the preamble is determined as an802.11ax preamble, and subsequent data is determined as a data packet of802.11ax. If the information is not the same, a protocol version of thepreamble is identified by using an existing method for automaticallydetecting a protocol version.

When an 802.11n/ac receive end receives the foregoing 802.11ax preamble,because both the two OFDM symbols following the L-SIG field aremodulated by using the BPSK, the 802.11n/ac receive end identifies apreamble and data of 802.11ax as a preamble and data of 802.11a, andperformance and compatibility of the 802.11n/ac receive end are alsounaffected.

FIG. 8 is a schematic block diagram of a transmit end device accordingto an embodiment of the present invention. A transmit end device 80 inFIG. 8 includes a generation unit 81 and a sending unit 82.

The generation unit 81 generates a preamble for a protocol version of awireless local area network, where the preamble includes a legacy signalL-SIG field and a high efficiency signal HE-SIG field that are arrangedin order, the HE-SIG field includes a first orthogonal frequencydivision multiplexing OFDM symbol and a second OFDM symbol that arearranged in order, and an input information bit of the first OFDM symbolis the same as that of the second OFDM symbol. The sending unit 82 sendsthe preamble to a receive end device.

When generating a preamble for a protocol version of a wireless localarea network, the transmit end device 80 in this embodiment of thepresent invention generates a first orthogonal frequency divisionmultiplexing OFDM symbol and a second OFDM symbol according to a sameinput information bit, and input information bits obtained after areceive end device restores the first OFDM symbol and the second OFDMsymbol can be the same, so that the receive end device determines thatthe preamble is the preamble of the protocol version, and rapid andreliable auto-detection of the 802.11ax version preamble can beimplemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection may be improved by using the first OFDM symbol and thesecond OFDM symbol that include a same bit sequence.

First, a transmit end device supporting a protocol version of thewireless local area network generates a to-be-transmitted preamble ofthe protocol version. Specifically, the transmit end device determinesan original information bit that needs to be carried in each field ofthe preamble, and performs processing such as channel coding,interleaving, and modulation on the original information bit, so as togenerate a preamble including multiple OFDM symbols. The followingembodiment mainly describes a generation process of an HE-SIG field thatfollows a legacy signal field L-SIG field in the preamble of theprotocol version. A generation process of a legacy part (an L-STF field,an L-LTF field, and the L-SIG field) of the preamble may be the same asthat in an existing older version protocol (such as 802.11a/n/ac).

It should be understood that the HE-SIG field includes at least twoparts. A first part immediately follows the L-SIG field, and a secondpart may be in any location of a non-legacy part. In a preferredembodiment, the second part may follow the HE-STF and the HE-LTF. Thisembodiment of the present invention mainly targets the first part of theHE-SIG field.

It should also be understood that this embodiment of the presentinvention does not limit a naming manner of the HE-SIG field, which maybe high efficiency (HE, High Efficiency), high efficiency wireless localarea network (HEW, High Efficiency WLAN), or the like.

Optionally, in an embodiment, the generation unit 81 is specificallyconfigured to process the input information bit by using a channelencoder, a first interleaver, and a first modulator to generate thefirst OFDM symbol, and process the input information bit by using thechannel encoder, a second interleaver, and a second modulator togenerate the second OFDM symbol, where the first interleaver and thesecond interleaver are different, and the first modulator and the secondmodulator are the same or different.

When generating the HE-SIG field, the transmit end device 80 may firstdetermine an initial bit sequence according to signaling informationthat needs to be carried in the HE-SIG field, then generates an inputinformation bit by sequentially capturing a bit sequence from theinitial bit sequence according to a quantity of bits that can be carriedin one OFDM symbol, and then processes the input information bit togenerate the first OFDM symbol and the second OFDM symbol.

Specifically, the input information bit may be scrambled first, channelcoding is performed by using the channel encoder, a sequence obtainedafter channel coding is interleaved by using the first interleaver andmodulated by using the first modulator in a first modulation manner, andoperations such as spatial flow shift, transformation to the timedomain, and guard interval addition are performed, so as to generate thefirst OFDM symbol.

Similarly, the input information bit may be scrambled first, channelcoding is performed by using the channel encoder, a sequence obtainedafter channel coding is interleaved by using the second interleaver andmodulated by using the second modulator in a second modulation manner,and operations such as spatial flow shift, transformation to the timedomain, and guard interval addition are performed, so as to generate thesecond OFDM symbol.

Both generation processes of the first OFDM symbol and the second OFDMsymbol include interleaving processing, but the first interleaver andthe second interleaver that perform interleaving processing aredifferent. In addition, modulation manners of the first OFDM symbol andthe second OFDM symbol may be the same or different, that is, the firstmodulator and the second modulator may be the same or different. In apreferred example, the modulation manner of the first OFDM symbol may beBPSK, and the modulation manner of the second OFDM symbol may also beBPSK; or the modulation manner of the first OFDM symbol is BPSK, and themodulation manner of the second OFDM symbol is QBPSK.

Optionally, in an embodiment, the generation unit 81 is specificallyconfigured to process the input information bit by using a channelencoder, an interleaver, and a first modulator to generate the firstOFDM symbol, and process the input information bit by using the channelencoder and a second modulator to generate the second OFDM symbol, wherethe first modulator and the second modulator are the same or different.Specifically, a generation process of the first OFDM symbol may includeinterleaving processing, and a generation process of the second OFDMsymbol may not include interleaving processing. Other processingprocesses are similar to those in the foregoing embodiment, and detailsare not described herein again.

Optionally, in an embodiment, the generation unit 81 is specificallyconfigured to process the input information bit by using a channelencoder and a first modulator to generate the first OFDM symbol, andprocess the input information bit by using the channel encoder, aninterleaver, and a second modulator to generate the second OFDM symbol,where the first modulator and the second modulator are the same ordifferent. Specifically, a generation process of the first OFDM symbolmay not include interleaving processing, and a generation process of thesecond OFDM symbol may include interleaving processing. Other processingprocesses are similar to those in the foregoing embodiment, and detailsare not described herein again.

Optionally, in an embodiment, the generation unit 81 is specificallyconfigured to process the input information bit by using a channelencoder and a first modulator to generate the first OFDM symbol, andprocess the input information bit by using the channel encoder and asecond modulator to generate the second OFDM symbol, where the firstmodulator and the second modulator are the same or different.Specifically, generation processes of the first OFDM symbol and thesecond OFDM symbol may neither include interleaving processing. Otherprocessing processes are similar to those in the foregoing embodiment,and details are not described herein again.

Optionally, in an embodiment, the generation unit 81 is specificallyconfigured to process the input information bit by using a channelencoder, an interleaver, and a first modulator to generate the firstOFDM symbol, and process the input information bit by using the channelencoder, the interleaver, and a second modulator to generate the secondOFDM symbol, where the first modulator and the second modulator are thesame or different. The first OFDM symbol and the second OFDM symbol passa same interleaver. Other processing processes are similar to those inthe foregoing embodiment, and details are not described herein again.

Optionally, in an embodiment, a subcarrier spacing used by the firstOFDM symbol and the second OFDM symbol is 312.5 kHz, and a guardinterval GI between the first OFDM symbol and the second OFDM symbol is0.8 μs. It should be understood that, to ensure compatibility with anexisting protocol version and unaffected performance of a receive end ofthe existing protocol version, an OFDM symbol in the HE-SIG field of thepreamble may use a subcarrier spacing and a guard interval that are thesame as those in the legacy field part.

Optionally, in an embodiment, the generation unit 81 is furtherconfigured to generate a third OFDM symbol that follows the second OFDMsymbol, where an input information bit of the third OFDM symbol includesa part or all of information bits, except the input information bit ofthe first OFDM symbol or the second OFDM symbol, in information bitsthat need to be carried in the HE-SIG field, a subcarrier spacing usedby the third symbol is 312.5 kHz, and a guard interval GI for the thirdOFDM symbol is 1.6 μs or 2.4 μs.

When the input information bit of the first OFDM symbol and the secondOFDM symbol includes only a part of the information bits that need to becarried in the HE-SIG field, the part or all of the information bits,except the input information bit of the first OFDM symbol or the secondOFDM symbol, in the information bits that need to be carried in theHE-SIG field may be carried in the third OFDM symbol.

That is, the third OFDM symbol that follows the second OFDM symbol maybe generated. Specifically, the input information bit of the third OFDMsymbol may be scrambled first, channel coding is performed by using thechannel encoder, a sequence obtained after channel coding isinterleaved, by using the same first interleaver used by the first OFDMsymbol, and modulated, and operations such as spatial flow shift,transformation to the time domain, and guard interval addition areperformed, so as to generate the third OFDM symbol. Preferably, amodulation manner of the third OFDM symbol may be BPSK or QBPSK. Theinterleaving manner of the third OFDM symbol may be the same as ordifferent from that of the first OFDM symbol, or may be the same as ordifferent from that of the second OFDM symbol. The guard interval of thethird OFDM symbol may be determined according to a protocol version ofthe foregoing preamble, that is, an 802.11ax protocol version maypredefine a symbol that follows the first OFDM symbol and the secondOFDM symbol, a field, and a guard interval of a data part. Preferably,the guard interval for the third OFDM symbol may be 1.6 μs or 2.4 μs.

Optionally, in an embodiment, the generation unit 81 is furtherconfigured to: generate a third OFDM symbol that follows the second OFDMsymbol, where an input information bit of the third OFDM symbol includesa part or all of information bits, except the input information bit ofthe first OFDM symbol or the second OFDM symbol, in information bitsthat need to be carried in the HE-SIG field; and generate a fourth OFDMsymbol that follows the third OFDM symbol, where an input informationbit of the fourth OFDM symbol is the same as the input information bitof the third OFDM symbol, a subcarrier spacing used by the third OFDMsymbol and the fourth OFDM symbol is 312.5 kHz, and a guard interval GIbetween the third OFDM symbol and the fourth OFDM symbol is 0.8 μs.

When the input information bit of the first OFDM symbol and the secondOFDM symbol includes only a part of the information bits that need to becarried in the HE-SIG field, the part or all of the information bits,except the input information bit of the first OFDM symbol or the secondOFDM symbol, in the information bits that need to be carried in theHE-SIG field may be carried in the third OFDM symbol and the fourth OFDMsymbol. Generation processes of the third OFDM symbol and the fourthOFDM symbol may be similar to the generation processes of the first OFDMsymbol and the second OFDM symbol, and details are not described herein.Preferably, interleaving and modulation manners of the third OFDM symbolare the same as those of the first OFDM symbol, and interleaving andmodulation manners of the fourth OFDM symbol are the same as those ofthe second OFDM symbol.

When generating a preamble for a protocol version of a wireless localarea network, the transmit end device 80 in this embodiment of thepresent invention generates a first orthogonal frequency divisionmultiplexing OFDM symbol and a second OFDM symbol according to a sameinput information bit, and input information bits obtained after areceive end device restores the first OFDM symbol and the second OFDMsymbol can be the same, so that the receive end device determines thatthe preamble is the preamble of the protocol version, and rapid andreliable auto-detection of the 802.11ax version preamble can beimplemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection may be improved by using the first OFDM symbol and thesecond OFDM symbol that include a same bit sequence. In addition, asubcarrier spacing and a guard interval that are used by the first OFDMsymbol and the second OFDM symbol are the same as a subcarrier spacingand a guard interval used in an existing protocol version. Therefore,normal reception of an 802.11ax preamble at a receive end of theexisting protocol version can be ensured, not affecting performance ofthe receive end of the existing protocol version.

FIG. 9 is a schematic block diagram of a receive end device according toan embodiment of the present invention. A receive end device 90 in FIG.9 includes a receiving unit 91, a restoration unit 92, and a determiningunit 93.

The receiving unit 91 receives a preamble sent by a transmit end devicefor a protocol version of a wireless local area network, where thepreamble includes a legacy signal L-SIG field and a high efficiencysignal HE-SIG field that are arranged in order, the HE-SIG fieldincludes a first orthogonal frequency division multiplexing OFDM symboland a second OFDM symbol that are arranged in order, and an inputinformation bit of the second OFDM symbol is the same as that of thefirst OFDM symbol. The restoration unit 92 restores the first OFDMsymbol and the second OFDM symbol that are in the HE-SIG field of thepreamble. The determining unit 93 determines that input information bitsobtained after the first OFDM symbol and the second OFDM symbol arerestored are the same, that is, determines that the preamble is apreamble of a first protocol version. The restoration unit 92 processesa remaining field of the preamble and a data part according to apredetermined rule of the protocol version.

The receive end device 90 in this embodiment of the present inventionreceives a preamble sent by the transmit end device 80 for a protocolversion of a wireless local area network, restores a first OFDM symboland a second OFDM symbol that are in an HE-SIG field of the preamble,and when determining that input information bits obtained afterrestoring the first OFDM symbol and the second OFDM symbol are the same,determines that the preamble is a preamble of a first protocol version.Rapid and reliable auto-detection of a preamble of an 802.11ax versioncan be implemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection may be improved by using the first OFDM symbol and thesecond OFDM symbol that include a same bit sequence.

First, a transmit end device supporting a protocol version of thewireless local area network generates a to-be-transmitted preamble ofthe protocol version. Specifically, the transmit end device determinesan original information bit that needs to be carried in each field ofthe preamble, and performs processing such as channel coding,interleaving, and modulation on the original information bit, so as togenerate a preamble including multiple OFDM symbols. The followingembodiment mainly describes a restoration process of an HE-SIG fieldthat follows a legacy signal field L-SIG field in the preamble of theprotocol version.

It should be understood that the HE-SIG field includes at least twoparts. A first part immediately follows the L-SIG field, and a secondpart may be in any location of a non-legacy part. In a preferredembodiment, the second part may follow an HE-STF and an HE-LTF. Thisembodiment of the present invention mainly targets the first part of theHE-SIG field.

It should also be understood that this embodiment of the presentinvention does not limit a naming manner of the HE-SIG field, which maybe high efficiency (HE, High Efficiency), high efficiency wireless localarea network (HEW, High Efficiency WLAN), or the like.

Optionally, in an embodiment, the restoration unit 92 is specificallyconfigured to process the first OFDM symbol by using a firstde-interleaver to generate a first sequence, and process the second OFDMsymbol by using a second de-interleaver to generate a second sequence,so as to determine that the first sequence and the second sequence arethe same, that is, to determine that the preamble is the preamble of thefirst protocol version, where the first de-interleaver and the secondde-interleaver are different.

When generating the HE-SIG field of the preamble, the transmit enddevice generates the first OFDM symbol and the second OFDM symbolaccording to a same input bit sequence. A process in which the receiveend device 90 restores the first OFDM symbol and the second OFDM symbolmay be considered as an inverse process of a generation processperformed by the transmit end device, that is, demodulation,de-interleaving, and decoding that are performed on the first OFDMsymbol and the second OFDM symbol by the receive end device 90 arecorresponding to modulation, interleaving, and encoding that areperformed on the first OFDM symbol and the second OFDM symbol by thetransmit end device. Specifically, the transmit end device generates thefirst OFDM symbol by using an encoder, a first modulator, and a firstinterleaver. A modulation manner corresponding to the first modulatormay be BPSK. Correspondingly, when restoring the first OFDM symbol, thereceive end device needs to de-interleave the first OFDM symbol by usinga first de-interleaver corresponding to the first interleaver. Thetransmit end device generates the second OFDM symbol by using the sameencoder and first modulator that are used to generate the first OFDMsymbol and a second interleaver that is different from the firstinterleaver used to generate the first OFDM symbol. Correspondingly,when restoring the second OFDM symbol, the receive end device needs tode-interleave the first OFDM symbol by using a second de-interleavercorresponding to the second interleaver. Then the de-interleaved firstOFDM symbol is compared with the de-interleaved second OFDM symbol, andif sequences are the same, the preamble may be determined as an 802.11axpreamble.

Optionally, in an embodiment, the restoration unit 92 is specificallyconfigured to process the first OFDM symbol by using a first demodulatorand a de-interleaver to generate a first sequence, and process thesecond OFDM symbol by using a second demodulator to generate a secondsequence, so as to determine that the first sequence and the secondsequence are the same, that is, to determine that the preamble is thepreamble of the first protocol version, where the first demodulator andthe second demodulator are the same or different.

Specifically, the transmit end device generates the first OFDM symbol byusing an encoder, a first modulator, and an interleaver. A modulationmanner corresponding to the first modulator may be BPSK.Correspondingly, when restoring the first OFDM symbol, the receive enddevice needs to de-interleave the first OFDM symbol by using ade-interleaver corresponding to the interleaver. The transmit end devicegenerates the second OFDM symbol by using the same encoder and secondmodulator that are used to generate the first OFDM symbol, andinterleaving is not performed. A modulation manner corresponding to thesecond modulator may be QBPSK. Correspondingly, when restoring thesecond OFDM symbol, the receive end device needs to rotate the OFDMsymbol 90 degrees clockwise by using the second demodulator. Then thede-interleaved first OFDM symbol is compared with the de-interleavedsecond OFDM symbol, and if sequences are the same, the preamble may bedetermined as an 802.11ax preamble.

Optionally, in an embodiment, the restoration unit 92 is specificallyconfigured to process the first OFDM symbol by using a first demodulatorto generate a first sequence, and process the second OFDM symbol byusing a second demodulator and a de-interleaver to generate a secondsequence, so as to determine that the first sequence and the secondsequence are the same, that is, to determine that the preamble is thepreamble of the first protocol version, where the first demodulator andthe second demodulator are the same or different.

Specifically, the transmit end device generates the first OFDM symbol byusing an encoder and a first modulator, and interleaving is notperformed. A modulation manner corresponding to the first modulator maybe BPSK. The transmit end device generates the second OFDM symbol byusing an encoder, a second modulator, and an interleaver. A modulationmanner corresponding to the second modulator may be QBPSK.Correspondingly, when restoring the second OFDM symbol, the receive enddevice needs to de-interleave the second OFDM symbol by using ade-interleaver corresponding to the interleaver and perform phaserotation on the second OFDM symbol by 90 degrees clockwise by using thesecond demodulator. Then the processed first OFDM symbol is comparedwith the de-interleaved and demodulated second OFDM symbol, and ifsequences are the same, the preamble may be determined as an 802.11axpreamble.

Optionally, in an embodiment, the restoration unit 92 is specificallyconfigured to process the first OFDM symbol by using a first demodulatorto generate a first sequence, and process the second OFDM symbol byusing a second demodulator to generate a second sequence, so as todetermine that the first sequence and the second sequence are the same,that is, to determine that the preamble is the preamble of the firstprotocol version, where the first demodulator and the second demodulatorare the same or different.

Optionally, in an embodiment, the restoration unit 92 is specificallyconfigured to process the first OFDM symbol by using a de-interleaver togenerate a first sequence, and process the second OFDM symbol by usingthe de-interleaver to generate a second sequence, so as to determinethat the first sequence and the second sequence are the same, that is,to determine that the preamble is the preamble of the first protocolversion.

Optionally, in an embodiment, a subcarrier spacing used by the firstOFDM symbol and the second OFDM symbol is 312.5 kHz, and a guardinterval GI between the first OFDM symbol and the second OFDM symbol is0.8 μs.

The receive end device 90 in this embodiment of the present inventionreceives a preamble sent by a transmit end device for a protocol versionof a wireless local area network, restores a first OFDM symbol and asecond OFDM symbol that are in an HE-SIG field of the preamble, and whendetermining that input information bits obtained after restoring thefirst OFDM symbol and the second OFDM symbol are the same, determinesthat the preamble is a preamble of a first protocol version. Rapid andreliable auto-detection of a preamble of an 802.11ax version can beimplemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection may be improved by using the first OFDM symbol and thesecond OFDM symbol that include a same bit sequence. In addition, asubcarrier spacing and a guard interval that are used by the first OFDMsymbol and the second OFDM symbol are the same as a subcarrier spacingand a guard interval used in an existing protocol version. Therefore,normal reception of an 802.11ax preamble at a receive end of theexisting protocol version can be ensured, not affecting performance ofthe receive end of the existing protocol version.

FIG. 10 is a structural block diagram of a transmit end device accordingto another embodiment of the present invention. A transmit end device100 in FIG. 10 includes a processor 101, a memory 102, a transmitcircuit 103, and an antenna 104.

The memory 102 is configured to store an instruction for the processor101 to execute the following operations: generating a preamble for aprotocol version of a wireless local area network, where the preambleincludes a legacy signal L-SIG field and a high efficiency signal HE-SIGfield that are arranged in order, the HE-SIG field includes a firstorthogonal frequency division multiplexing OFDM symbol and a second OFDMsymbol that are arranged in order, and an input information bit of thefirst OFDM symbol is the same as that of the second OFDM symbol; andsending the preamble to a receive end device by using the transmitcircuit 103, so that the receive end device restores the preamble, andwhen determining that input information bits obtained after restoringthe first OFDM symbol and the second OFDM symbol are the same,determines that the preamble is the preamble of the protocol version.

When generating a preamble for a protocol version of a wireless localarea network, the transmit end device 100 in this embodiment of thepresent invention generates a first orthogonal frequency divisionmultiplexing OFDM symbol and a second OFDM symbol according to a sameinput information bit, and input information bits obtained after areceive end device restores the first OFDM symbol and the second OFDMsymbol can be the same, so that the receive end device determines thatthe preamble is the preamble of the protocol version, and rapid andreliable auto-detection of the 802.11ax version preamble can beimplemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection may be improved by using the first OFDM symbol and thesecond OFDM symbol that include a same bit sequence.

In addition, the transmit end device 100 may further include a receivecircuit 105, a bus 106, and the like. The processor 101 controls anoperation of the transmit end device 100, and the processor 101 may alsobe referred to as a CPU (Central Processing Unit, central processingunit). The memory 102 may include a read-only memory and a random accessmemory, and provide an instruction and data for the processor 101. Apart of the memory 102 may further include a non-volatile random accessmemory (NVRAM). In specific application, the transmit circuit 103 andthe receive circuit 105 may be coupled to the antenna 104. Components ofthe transmit end device 100 are coupled together by using the bus system106. The bus system 106 may further includes a power bus, a control bus,a status signal bus, and the like, in addition to a data bus. However,for clarity of description, various buses are marked as the bus system106 in the figure.

The method disclosed in the foregoing embodiments of the presentinvention may be applied to the processor 101, or implemented by theprocessor 101. The processor 101 may be an integrated circuit chip andhas a signal processing capability. In an implementation process, thesteps in the foregoing method may be completed by using an integratedlogic circuit of hardware in the processor 101 or an instruction in aform of software. The processor 101 may be a general processor, adigital signal processor (DSP), an application-specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or anotherprogrammable logic device, a discrete gate or transistor logic device,or a discrete hardware assembly. The processor 101 may implement orexecute the methods, steps, and logical block diagrams disclosed in theembodiments of the present invention. The general-purpose processor maybe a microprocessor or the processor may be any conventional processor,or the like. The steps of the method disclosed with reference to theembodiments of the present invention may be directly performed andcompleted by using a hardware decoding processor, or performed andcompleted by combining hardware and software modules in a decodingprocessor. The software module may be located in a mature storage mediumin the art, such as a random access memory, a flash memory, a read-onlymemory, a programmable read-only memory, an electrically erasableprogrammable memory, or a register. The storage medium is located in thememory 102. The processor 101 reads information in the memory 102, andcompletes the steps of the foregoing method in combination with hardwareof the memory 102.

FIG. 11 is a structural block diagram of a receive end device accordingto another embodiment of the present invention. A receive end device noin FIG. 11 includes a processor 111, a memory 112, a receive circuit113, and an antenna 114.

The memory 102 is configured to store an instruction for the processor101 to execute the following operations: receiving, by using the receivecircuit 113, a preamble sent by a transmit end device for a protocolversion of a wireless local area network, where the preamble includes alegacy signal L-SIG field and a high efficiency signal HE-SIG field thatare arranged in order, the HE-SIG field includes a first orthogonalfrequency division multiplexing OFDM symbol and a second OFDM symbolthat are arranged in order, and an input information bit of the secondOFDM symbol is the same as that of the first OFDM symbol; restoring thefirst OFDM symbol and the second OFDM symbol that are in the HE-SIGfield of the preamble; determining that sequences obtained after thefirst OFDM symbol and the second OFDM symbol are restored are the same;and restoring a remaining field of the preamble and a data partaccording to a predetermined rule of the protocol version.

The receive end device no in this embodiment of the present inventionreceives a preamble sent by a transmit end device for a protocol versionof a wireless local area network, restores a first OFDM symbol and asecond OFDM symbol that are in an HE-SIG field of the preamble, and whendetermining that input information bits obtained after restoring thefirst OFDM symbol and the second OFDM symbol are the same, determinesthat the preamble is a preamble of a first protocol version. Rapid andreliable auto-detection of a preamble of an 802.11ax version can beimplemented. In addition, when 802.11ax is applied to an outdoorscenario, reliability and correctness of preamble transmission andauto-detection may be improved by using the first OFDM symbol and thesecond OFDM symbol that include a same bit sequence.

In addition, the receive end device no may further include a transmitcircuit 115, a bus 116, and the like. The processor 111 controls anoperation of the receive end device no, and the processor 111 may alsobe referred to as a CPU (Central Processing Unit, central processingunit). The memory 112 may include a read-only memory and a random accessmemory, and provide an instruction and data for the processor 111. Apart of the memory 112 may further include a non-volatile random accessmemory (NVRAM). In specific application, the receive circuit 113 and thetransmit circuit 115 may be coupled to the antenna 114. Components ofthe receive end device no are coupled together by using the bus system116. The bus system 116 may further includes a power bus, a control bus,a status signal bus, and the like, in addition to a data bus. However,for clarity of description, various buses are marked as the bus system116 in the figure.

The method disclosed in the foregoing embodiments of the presentinvention may be applied to the processor 111, or implemented by theprocessor 111. The processor 111 may be an integrated circuit chip andhas a signal processing capability. In an implementation process, thesteps in the foregoing method may be completed by using an integratedlogic circuit of hardware in the processor 111 or an instruction in aform of software. The processor 111 may be a general processor, adigital signal processor (DSP), an application-specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or anotherprogrammable logic device, a discrete gate or transistor logic device,or a discrete hardware assembly. The processor 111 may implement orexecute the methods, steps, and logical block diagrams disclosed in theembodiments of the present invention. The general-purpose processor maybe a microprocessor or the processor may be any conventional processor,or the like. The steps of the method disclosed with reference to theembodiments of the present invention may be directly performed andcompleted by using a hardware decoding processor, or performed andcompleted by combining hardware and software modules in a decodingprocessor. The software module may be located in a mature storage mediumin the art, such as a random access memory, a flash memory, a read-onlymemory, a programmable read-only memory, an electrically erasableprogrammable memory, or a register. The storage medium is located in thememory 112. The processor in reads information in the memory 112, andcompletes the steps of the foregoing method in combination with hardwareof the memory 112.

A person skilled in the art may understand that possible replacementsmay be made to solutions in the foregoing implementation manners. Forexample, a first OFDM symbol and a second OFDM symbol that are in apreamble may be symbols in another field such as symbols in a legacysignal L-SIG field. As long as input information bits of the first OFDMsymbol and the second OFDM symbol are the same, a protocol version ofthe preamble may be obtained according to these two OFDM symbols, andapplication of a specific process of generating these two OFDM symbolsin the foregoing implementation manners is unaffected. Specifically, howto obtain the first OFDM symbol and the second OFDM symbol by processingthe same input information bit is not limited. In addition, the preamblein the foregoing implementation manners may have another possibletransformation. For example, another field exists between a legacysignal L-SIG field and an HE-SIG field; or in some cases, for example,an uplink preamble does not include an HE-SIG field.

In addition, according to some preferred implementation manners ofgenerating these two OFDM symbols in the foregoing implementationmanners, time domain signals of these two generated OFDM symbols aredifferent. In this way, a frequency selectivity gain may be obtainedwhen the receive end performs combined reception, so that a bit errorrate is reduced.

The foregoing provides multiple implementation manners of generating thefirst OFDM symbol and the second OFDM symbol, and alternatively, thegenerating a preamble for a protocol version of a wireless local areanetwork may include:

processing the input information bit by using a channel encoder, aninterleaver, and a first modulator, and performing subcarrier mapping ina first order to generate the first OFDM symbol; and

processing the input information bit by using the channel encoder, theinterleaver, and a second modulator, and performing subcarrier mappingin a second order to generate the second OFDM symbol, where

the first modulator and the second modulator are the same or different,and the first order and the second order are different.

The following describes several possible specific examples. In aspecific example, a transmit end generates a preamble that includes alegacy preamble part that conforms to an 802.11n/ac standard and anHEW-SIG1 field that conforms to 802.11ax. The HEW-SIG1 field includestwo consecutive OFDM symbols. A first OFDM symbol in the HEW-SIG1 fielduses a subcarrier spacing of 312.5 kHz and a GI of 0.8 μs. An inputinformation bit carried in the first OFDM symbol is processed by using achannel encoder and an interleaver and then modulated by using BPSK.Then a modulation symbol is sequentially mapped to all subcarriers. Asecond OFDM symbol in the HEW-SIG1 field uses the subcarrier spacing of312.5 kHz and the GI of 0.8 μs. An input information bit carried in thesecond OFDM symbol is the same as the input information bit carried inthe first OFDM symbol in the HEW-SIG1 field, and is processed by usingthe channel encoder and the interleaver and then modulated by using theBPSK. Then a modulation symbol is mapped to all subcarriers in areversed order.

After the second OFDM symbol in the HEW-SIG1 field is sent, a subsequentOFDM symbol (including a remaining field of the preamble that conformsto 802.11ax, and a data field) may be sent by using a subcarrier spacingof 312.5 kHz or another value and a GI of 0.8 μs or another value. Thisis not limited herein.

Correspondingly, at a receive end that conforms to an 802.11ax standard,

001 a. Perform channel equalization on a first OFDM symbol and a secondOFDM symbol that follow a received legacy preamble (such as an SIG/L-SIGfield) to obtain a first frequency domain sequence and a secondfrequency domain sequence, respectively, and cache the first frequencydomain sequence and the second frequency domain sequence.

002 a. Demap the first frequency domain sequence according to a firstorder to obtain a third frequency domain sequence, demap the secondfrequency domain sequence according to a second order to obtain a fourthfrequency domain sequence, and then determine whether the thirdfrequency domain sequence and the fourth frequency domain sequence arethe same. If the third frequency domain sequence and the fourthfrequency domain sequence are the same, the data packet is considered asan 802.11ax data packet. Go to step 003. If the third frequency domainsequence and the fourth frequency domain sequence are not the same, thedata packet is not an 802.11ax data packet. Return to step 001 in whichthe first frequency domain sequence and the second frequency domainsequence are cached. A protocol version of the data packet is furtheridentified according to the prior art or another technology (such as anauto-detection method defined in the 802.11n/ac standard).

003 a. Perform soft-bit combination on information carried insubcarriers corresponding to the third frequency domain sequence and thefourth frequency domain sequence, and then perform processing such asdecoding according to the 802.11ax standard.

004 a. Receive a subsequent OFDM symbol (including a remaining part ofthe preamble and a data part) according to a subcarrier spacing and a GIthat are corresponding to a transmit end.

For a receive end that conforms to the 802.11n/ac standard but does notconform to the 802.11ax standard, because two OFDM symbols of theHEW-SIG1 field that follow the L-SIG field of the preamble are modulatedby using the BPSK, the 11n/ac receive end processes an 802.11ax datapacket in a manner of processing an 802.11a data packet, and backwardcompatibility is unaffected.

A person skilled in the art learns that the foregoing HEW-SIG1 may alsobe referred to as an HE-SIG-A. All implementation manners may be appliedto not only the HE-SIG-A but also another possible pilot field, and thelike. In an alternative preferred implementation manner, as shown inFIG. 15, an HE-SIG-A field includes two OFDM symbols, and at a transmitend (which, for example, conforms to 802.11ax) in a wireless local areanetwork, the method includes the following steps: 1501. Generate a firstOFDM symbol in the HE-SIG-A field, where the symbol may use a subcarrierspacing of 312.5 kHz and a GI of 0.8 μs, an information bit carried inthe first OFDM symbol is processed by using a channel encoder Channelcoding and an interleaver Interleaver and then modulated by using afirst modulator such as a BPSK modulator. Then a generated modulationsymbol is mapped to all data subcarriers according to a first ordershown in the following formula. The first OFDM symbol (an HE-SIG-A1) ofthe HE-SIG-A field shown in FIG. 15 is obtained after other subsequentprocessing.

The k^(th) modulation symbol is mapped to the t^(th) data subcarrieraccording to t(k)=k, k=0, 1, . . . N_(SD)−1 (formula 1) and IDFTtransform is performed, so as to generate the second OFDM symbol.

N_(SD) indicates a quantity of data subcarriers. For example, when abandwidth is 20 MHz, N_(SD) may be 48 or 52.

In this case, mapping in the first order is equivalent to directsequential mapping.

1502. Generate a second OFDM symbol in the HE-SIG-A field aftergenerating the first OFDM symbol in the HE-SIG-A field, where the secondOFDM symbol may use the subcarrier spacing of 312.5 kHz and the GI of0.8 μs, and an information bit carried in the second OFDM symbol is thesame as the information bit carried in the first OFDM symbol in theHE-SIG-A field, and is processed by using the channel encoder Channelcoding and the interleaver Interleaver and then modulated by using asecond modulator such as the BPSK modulator. The second modulator andthe first modulator are the same or different (for example, the secondmodulator may be a QBPSK modulator). Then a generated modulation symbolis mapped to all data subcarriers according to a second order shown informula 2:t(k)=N _(COL) *k−(N _(SD)−1)*└k/N _(ROW) ┘,k=0,1, . . . N_(SD)−1  (formula 2),

that is, the k^(th) modulation symbol is mapped to the t^(th) datasubcarrier and IDFT transform is performed. When N_(SD)=48, N_(COL) maybe 16 and N_(ROW) may be 3. When N_(SD)=52, N_(COL) may be 13 andN_(ROW) may be 4.

It should be understood that when the second modulator uses BPSK orQBPSK modulation, a technical effect of mapping the generated modulationsymbol to all the data subcarriers according to the second order is thesame as a technical effect of performing BPSK or QBPSK modulation on acarried information bit immediately after the carried information bit isprocessed by using the channel encoder, and directly and sequentiallymapping a generated modulation symbol to all the data subcarriers.

Specifically, the mapping in the second order is the same as a step 3 ofa sorting operation (formula 2) that is in a de-interleaving operationperformed by a receive end and that is specified in an existing standardsuch as 802.11n or 802.11ac. A module in an existing receiving unit maybe reused in actual implementation, so that the implementation becomeseasier without raising a bit error rate. If the second modulator useshigher-order modulation such as 16QAM or 64QAM, because the step 3 ofthe sorting operation (formula 2) that is in the de-interleavingoperation performed by the receive end and that is specified in theexisting standard is irrelevant to a modulation order, a mappingoperation may be still performed by directly using the second orderdescribed in formula 2, and extensibility is good.

It should be understood that if the HE-SIG-A field includes four OFDMsymbols, a third OFDM symbol and a fourth OFDM symbol may be generatedby using similar steps.

It should be understood that if a transmission bandwidth is greater than20 MHz, such as 40 MHz, 80 MHz, or 160 MHz, after subcarrier mapping isperformed in the first order or the second order, a subcarrier signalgenerated on a 20 MHz bandwidth is copied to all 20 MHz sub-channels ofthe transmission bandwidth, and then IDFT transform is performed.

Correspondingly, at a receive end (for example, of 802.11ax) in thewireless local area network,

1601. Perform channel equalization on a first OFDM symbol and a secondOFDM symbol that are in an HE-SIG-A field to obtain a frequency domainsequence 1 and a frequency domain sequence 2, and cache the frequencydomain sequence 1 and the frequency domain sequence 2.

1602. Demap the frequency domain sequence 1 according to a first orderto obtain a frequency domain sequence 3, that is,

perform a demapping operation directly and sequentially or according tok(t)=t, t=0, 1, . . . N_(SD)−1 (formula 3) to obtain a frequency domainsequence 3.

1603. Demap the frequency domain sequence 2 according to a second orderto obtain a frequency domain sequence 4, that is, obtain a frequencydomain sequence 4 according tok(t)=N _(ROW)*(t mod N _(COL))+└t/N _(COL) ┘,t=0,1, . . . N_(SD)−1  (formula 4).

1604. Perform BPSK demodulation on the frequency domain sequence 3 andthe frequency domain sequence 4, perform soft-bit combination, andperform decoding according to an existing standard.

In an alternative preferred implementation manner, as shown in FIG. 16,an HE-SIG-A field includes two OFDM symbols, and at a transmit end(which, for example, conforms to 802.11ax) in a wireless local areanetwork, the method includes the following steps:

1701. Similar to step 1501 in the previous implementation manner,generate a first OFDM symbol in the HE-SIG-A field, where the symbol mayuse a subcarrier spacing of 312.5 kHz and a GI of 0.8 μs, and aninformation bit carried in the first OFDM symbol is processed by using achannel encoder Channel coding and an interleaver Interleaver and thenmodulated by using a first modulator such as a BPSK modulator. Then agenerated modulation symbol is mapped to all data subcarriers accordingto a first order shown in the following formula. The first OFDM symbol(an HE-SIG-A1) of the HE-SIG-A field shown in FIG. 16 is obtained afterother subsequent processing.

The k^(th) modulation symbol is mapped to the t^(th) data subcarrieraccording to t(k)=k, k=0, 1, . . . N_(SD)−1 (formula 1) and IDFTtransform is performed, so as to generate the first OFDM symbol.

N_(SD) indicates a quantity of data subcarriers, and when a bandwidth is20 MHz, N_(SD) may be 48 or 52.

In this case, mapping in the first order is equivalent to directsequential mapping.

1702. Generate a second OFDM symbol in the HE-SIG-A field aftergenerating the first OFDM symbol in the HE-SIG-A field, where the symbolmay use the subcarrier spacing of 312.5 kHz and the GI of 0.8 μs, and aninformation bit carried in the second OFDM symbol is the same as theinformation bit carried in the first OFDM symbol in the HE-SIG-A field,and is processed by using the channel encoder and the interleaver andthen modulated by using a second modulator such as the BPSK modulator.The second modulator and the first modulator are the same or different(for example, the second modulator may be a QBPSK modulator). Then agenerated modulation symbol is mapped to all data subcarriers accordingto a second order shown in formula 5:t(k)=N _(ROW)*(k mod N _(COL))+└k/N _(COL) ┘,k=0,1, . . . N_(SD)−1  (formula 5),

that is, the k^(th) modulation symbol is mapped to the t^(th) datasubcarrier and IDFT transform is performed. When N_(SD)=48, N_(COL) maybe 16 and N_(ROW) may be 3. When N_(SD)=52, N_(COL) may be 13 andN_(ROW) may be 4.

It should be understood that when the second modulator uses BPSK orQBPSK modulation, a technical effect of mapping the generated modulationsymbol to all the data subcarriers according to the second order is thesame as a technical effect of performing BPSK or QBPSK modulation on acarried information bit immediately after the carried information bit isprocessed by using the channel encoder and the interleaver, andsequentially mapping the generated modulation symbol to all the datasubcarriers after the generated modulation symbol is processed by usingthe interleaver again.

The mapping in the second order is the same as a step 1 of a sortingoperation (formula 5) that is in an interleaving operation performed bya transmit end and that is specified in an existing standard. Aninterleaver module in an existing sending unit may be reused in actualimplementation, so that the implementation becomes easier withoutraising a bit error rate.

If the second modulator uses higher-order modulation such as 16QAM or64QAM, because the step 1 of the sorting operation that is in theinterleaving operation performed by the transmit end and that isspecified in the existing standard is irrelevant to a modulation order,a mapping operation may be still performed by directly using the secondorder described in the formula, and extensibility is good.

Correspondingly, at a receive end (of, such as, 802.11ax) in thewireless local area network,

1801. Referring to step 1601, perform channel equalization on a firstOFDM symbol and a second OFDM symbol that are in an HE-SIG-A field toobtain a frequency domain sequence 1 and a frequency domain sequence 2,and cache the frequency domain sequence 1 and the frequency domainsequence 2.

1802. Demap the frequency domain sequence 1 according to a first orderto obtain a frequency domain sequence 3, that is,

perform a demapping operation according to k(t)=t, t=0, 1, . . .N_(SD)−1 (formula 6) to obtain a frequency domain sequence 3.

1803. Demap the frequency domain sequence 2 according to a second orderto obtain a frequency domain sequence 4, that is,

perform a demapping operation according tok(t)=N_(COL)*t−(N_(SD)−1)*└t/N_(ROW) ┘, t=0, 1, . . . N_(SD)−1 (formula7) to obtain a frequency domain sequence 4.

1804. Perform BPSK demodulation on the frequency domain sequence 3 andthe frequency domain sequence 4, perform soft-bit combination, andperform decoding according to an existing standard.

In an alternative preferred implementation manner, as shown in FIG. 17,an HE-SIG-A field includes two OFDM symbols, and at a transmit end(which, for example, conforms to 802.11ax) in a wireless local areanetwork, the method includes the following steps: 1901. Generate a firstOFDM symbol in the HE-SIG-A field, where the symbol may use a subcarrierspacing of 312.5 kHz and a GI of 0.8 μs, an information bit carried inthe first OFDM symbol is processed by using a channel encoder and aninterleaver and then modulated by using a first modulator such as a BPSKmodulator. Then a generated modulation symbol is mapped to all datasubcarriers according to a first order shown in the following formula:t(k)=N _(ROW)*(k mod N _(COL))+└k/N _(COL) ┘,k=0,1, . . . N_(SD)−1  (formula 8),

that is, the k^(th) modulation symbol is mapped to the t^(th) datasubcarrier and IDFT transform is performed. N_(SD) indicates a quantityof data subcarriers, and when a bandwidth is 20 MHz, N_(SD) may be 48 or52. When N_(SD)=48, N_(COL) may be 16 and N_(ROW) may be 3. WhenN_(SD)=52, N_(COL) may be 13 and N_(ROW) may be 4.

1902. Generate a second OFDM symbol in the HE-SIG-A field aftergenerating the first OFDM symbol in the HE-SIG-A field, where the secondOFDM symbol may use the subcarrier spacing of 312.5 kHz and the GI of0.8 μs, and an information bit carried in the second OFDM symbol is thesame as the information bit carried in the first OFDM symbol in theHE-SIG-A field, and is processed by using the channel encoder and theinterleaver and then modulated by using a second modulator such as theBPSK modulator. The second modulator and the first modulator are thesame or different (for example, the second modulator may be a QBPSKmodulator). Then a generated modulation symbol is mapped to all datasubcarriers according to a second order shown in the following formula:t(k)=N _(COL) *k−(N _(SD)−1)*└k/N _(ROW) ┘,k=0,1, . . . N_(SD)−1  (formula 9),

that is, the k^(th) modulation symbol is mapped to the t^(th) datasubcarrier and IDFT transform is performed. When N_(SD)=48, N_(COL) maybe 16 and N_(ROW) may be 3. When N_(SD)=52, N_(COL) may be 13 andN_(ROW) may be 4.

Correspondingly, at a receive end (of, such as, 802.11ax) in thewireless local area network,

2001. Perform channel equalization on a first OFDM symbol and a secondOFDM symbol that are in an HE-SIG-A field to obtain a frequency domainsequence 1 and a frequency domain sequence 2, and cache the frequencydomain sequence 1 and the frequency domain sequence 2.

2002. Demap the frequency domain sequence 1 according to a first orderto obtain a frequency domain sequence 3, that is,

perform a demapping operation according tok(t)=N_(COL)*t−(N_(SD)−1)*└t/N_(ROW) ┘, t=0, 1, . . . N_(SD)−1 (formula10) to obtain a frequency domain sequence 3.

2003. Demap the frequency domain sequence 2 according to a second orderto obtain a frequency domain sequence 4, that is,

perform a demapping operation according to k(t)=N_(ROW)*(t modN_(COL))+└t/N_(COL)┘, t=0, 1, . . . N_(SD)−1 (formula 11) to obtain afrequency domain sequence 4, where t is an index of a data subcarrierafter mapping and k is an index of a modulation symbol.

2004. Perform BPSK demodulation on the frequency domain sequence 3 andthe frequency domain sequence 4, perform soft-bit combination, andperform decoding according to an existing standard.

In another specific implementation manner, an 802.11ax transmit endgenerates a preamble. As shown in FIG. 12, the preamble includes: anL-STF field and an L-LTF field that conform to an 11n/ac standard, anL-SIG field, and an HEW-SIG1 field of 802.11ax. A first OFDM symbol inthe L-SIG field conforms to an 11n/ac standard and uses a subcarrierspacing of 312.5 kHz and a GI of 0.8 μs. An information bit carried inthe first OFDM symbol is processed by using a channel encoder and afirst interleaver and then modulated by using BPSK. A second OFDM symbolin the L-SIG field uses the subcarrier spacing of 312.5 kHz and the GIof 0.8 μs. An information bit carried in the second OFDM symbol is thesame as the input information bit carried in the first OFDM symbol inthe L-SIG field, and is processed by using the channel encoder and asecond interleaver (or interleaving may be not performed) and thenmodulated by using the BPSK.

A symbol (including a remaining field of the preamble and a data field)that follows the second OFDM symbol in the L-SIG field may be sent byusing a subcarrier spacing of 312.5 kHz or another value and a GI of 0.8μs or another value.

Correspondingly, at a receive end,

001 b. Perform channel equalization on the first OFDM symbol and thesecond OFDM symbol that are in the L-SIG field to obtain a firstfrequency domain sequence and a second frequency domain sequence,respectively, and cache the first frequency domain sequence and thesecond frequency domain sequence.

002 b. Perform de-interleaving on the first frequency domain sequence byusing a first de-interleaver to obtain a third frequency domainsequence, and perform (or do not perform) de-interleaving on the secondfrequency domain sequence by using a second de-interleaver to obtain afourth frequency domain sequence; then determine whether informationcarried in a subcarrier corresponding to the third frequency domainsequence is the same as information carried in a subcarriercorresponding to the fourth frequency domain sequence. If theinformation is the same, the data packet is considered as an 802.11axdata packet. Go to step 003 b. If the information is not the same, thedata packet is not an 802.11ax data packet. Return to step 001 b inwhich the first frequency domain sequence and the second frequencydomain sequence are cached. A mode of the data packet is identified byusing an auto-detection method in the prior art.

003 b. Perform soft-bit combination on the information carried in thesubcarriers corresponding to the third frequency domain sequence and thefourth frequency domain sequence, and then perform decoding according tothe 802.11ax standard.

A subsequent OFDM symbol (including a remaining part of the preamble anda data part) is received according to a subcarrier spacing and a GI thatare corresponding to the transmit end.

For an 11n receive end, because the second OFDM symbol in the L-SIGfield of the preamble is modulated by using the BPSK, the 11n receiveend processes an 11ax data packet in a manner of processing an 11a datapacket, thereby not affecting backward compatibility.

For an 11ac receive end, because the second OFDM symbol in the L-SIGfield of the preamble is modulated by using the BPSK, the 11ac receiveend processes an 11ax data packet in a manner of processing an 11a datapacket or a manner of processing an 11ac data packet. If the 11ax datapacket is processed in the manner of processing the 11a data packet, CRCverification fails after full deframing, and backward compatibility isunaffected. If the 11ax data packet is processed in the manner ofprocessing the 11ac data packet, CTC verification fails after a VHT-SIGAis demodulated, and an 11ac receiver performs backoff according to aframe length indicated in the L-SIG, thereby not affecting backwardcompatibility.

In another specific implementation manner, an 802.11ax transmit endgenerates a preamble. Referring to FIG. 13, the preamble includes: anL-STF field and an L-LTF field that conform to an 11n/ac standard, andan L-SIG field and an HEW-SIG1 field that are of 802.11ax. The L-SIGfield includes two OFDM symbols. A first OFDM symbol in the L-SIG fielduses a subcarrier spacing of 312.5 kHz and a GI of 0.8 μs, and an inputinformation bit carried in the first OFDM symbol is processed by using achannel encoder and an interleaver and then modulated by using BPSK.Then a modulation symbol is sequentially mapped to all subcarriers. Asecond OFDM symbol in the L-SIG field uses the subcarrier spacing of312.5 kHz and the GI of 0.8 μs. An input information bit carried in thesecond OFDM symbol is the same as the input information bit carried inthe first OFDM symbol in the L-SIG field, and is processed by using thechannel encoder and the interleaver and then modulated by using theBPSK. Then a modulation symbol is mapped to all subcarriers in areversed order.

After the second OFDM symbol in the L-SIG field is sent, a subsequentOFDM symbol (including a remaining field of the preamble and a datafield) may be sent by using a subcarrier spacing of 312.5 kHz or anothervalue and a GI of 0.8 μs or another value.

At a receive end,

001 c. Perform channel equalization on a first OFDM symbol and a secondOFDM symbol that are in a received L-SIG field to obtain a firstfrequency domain sequence and a second frequency domain sequence,respectively, and cache the first frequency domain sequence and thesecond frequency domain sequence.

002 c. Demap the first frequency domain sequence according to a firstorder to obtain a third frequency domain sequence, demap the secondfrequency domain sequence according to a second order to obtain a fourthfrequency domain sequence, and then determine whether informationcarried in a subcarrier corresponding to the third frequency domainsequence is the same as information carried in a subcarriercorresponding to the fourth frequency domain sequence. If theinformation is the same, the data packet is considered as an 802.11axdata packet. Go to step 003 c. If the information is not the same, thedata packet is not an 802.11ax data packet. Return to step 001 c inwhich the first frequency domain sequence and the second frequencydomain sequence are cached. A mode of the data packet is identified byusing an auto-detection method in the prior art.

003 c. Perform soft-bit combination on the information carried in thesubcarriers corresponding to the third frequency domain sequence and thefourth frequency domain sequence, and then perform decoding according tothe 802.11ax standard.

A subsequent OFDM symbol (including a remaining part of the preamble anda data part) is received according to a subcarrier spacing and a GI thatare corresponding to the transmit end.

For an 802.11n receive end, because the second OFDM symbol in the L-SIGfield of the preamble is modulated by using the BPSK, the 802.11nreceive end processes an 11ax data packet in a manner of processing an11a data packet, and backward compatibility is unaffected.

For an 802.11ac receive end, because the second OFDM symbol in the L-SIGfield of the preamble is modulated by using the BPSK, the 802.11acreceive end processes an 802.11ax data packet in a manner of processingan 802.11a data packet or a manner of processing an 802.11ac datapacket. If the 802.11ax data packet is processed in the manner ofprocessing the 802.11a data packet, CRC verification fails after fulldeframing, not affecting backward compatibility. If the 802.11ax datapacket is processed in the manner of processing the 802.11ac datapacket, CTC verification fails after a VHT-SIGA is demodulated, and an802.11ac receiver performs backoff according to a frame length indicatedin the L-SIG, thereby not affecting backward compatibility.

In another preferred implementation manner, an 802.11ax transmit endgenerates and sends a preamble. Referring to FIG. 14, an L-SIG field ofthe preamble includes two OFDM symbols, and an HE-SIGs of the preambleincludes at least one OFDM symbol.

Input information bits of a first OFDM symbol and a second OFDM symbolthat are in the L-SIG field are the same. For a generation manner of thefirst OFDM symbol and the second OFDM symbol, refer to the foregoingembodiments.

After sending the second OFDM symbol in the L-SIG field, the transmitend sends a first OFDM symbol of the HE-SIG1 field. The symbol uses asubcarrier spacing of Δf=312.5 kHz and a guard interval of T_(GI)=1.6μs, an information bit carried in the first OFDM symbol is processed byusing a channel encoder and an interleaver and then modulated by usingBPSK.

Specifically, a transmission waveform formula of the first OFDM symbolin the HE-SIG1 field is as follows:

${{r_{{HE} - {{SIG}\; 1_{1{st}}}}(t)} = {{w_{T}(t)}{\sum\limits_{k = {{- N_{ST}}/2}}^{N_{ST}/2}\;{C_{k}{\exp\left( {{j2}\;\pi\; k\;\Delta\; f} \right)}\left( {t - T_{{post} - {fix}}} \right)}}}},$

where N_(ST) is a quantity of available data plus a quantity of pilotsubcarriers, C_(k) is a modulation symbol carried in each subcarrier,Δf=312.5 kHz is a subcarrier spacing, T_(post-fix)=0.8 μs generates acyclic prefix of 0.8 μs, and w_(T)(t) may be but is not limited to awindow function recommended in an existing standard, where duration ofw_(T)(t) is

$T = {{\frac{1}{\Delta\; f} + T_{GI}} = {4.8\mspace{14mu}{{µs}.}}}$

The cyclic prefix T_(post-fix) and the guard interval T_(GI) may takeother values as long as the cyclic prefix T_(post-fix) is less than orequal to the guard interval T_(GI). The subcarrier spacing may takeanother value such as Δf=312.5 kHz.

After the first OFDM symbol in the HE-SIG1 field is sent, a subsequentOFDM symbol (including a remaining field of the preamble and a datafield) may be sent by using a subcarrier spacing of 312.5 kHz or anothervalue and a GI of 0.8 μs or another value.

The term “and/or” in this specification describes only an associationrelationship for describing associated objects and represents that threerelationships may exist. For example, A and/or B may represent thefollowing three cases: Only A exists, both A and B exist, and only Bexists. In addition, the character “/” in this specification generallyindicates an “or” relationship between the associated objects.

It should be understood that sequence numbers of the foregoing processesdo not mean execution sequences in various embodiments of the presentinvention. The execution sequences of the processes should be determinedaccording to functions and internal logic of the processes, and shouldnot be construed as any limitation on the implementation processes ofthe embodiments of the present invention.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraint conditions ofthe technical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of the present invention.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, reference may bemade to a corresponding process in the foregoing method embodiments, anddetails are not described herein again.

In the several embodiments provided in the present application, itshould be understood that the disclosed system, apparatus, and methodmay be implemented in other manners. For example, the describedapparatus embodiment is merely exemplary. For example, the unit divisionis merely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected according toactual needs to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of the presentinvention may be integrated into one processing unit, or each of theunits may exist alone physically, or two or more units are integratedinto one unit.

When the functions are implemented in the form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer-readable storage medium. Based on such anunderstanding, the technical solutions of the present inventionessentially, or the part contributing to the prior art, or some of thetechnical solutions may be implemented in a form of a software product.The software product is stored in a storage medium, and includes severalinstructions for instructing a computer device (which may be a personalcomputer, a server, or a network device) to perform all or some of thesteps of the methods described in the embodiments of the presentinvention. The foregoing storage medium includes: any medium that canstore program code, such as a USB flash drive, a removable hard disk, aread-only memory (ROM, Read-Only Memory), a random access memory (RAM,Random Access Memory), a magnetic disk, or an optical disc.

The foregoing descriptions are merely specific implementation manners ofthe present invention, but are not intended to limit the protectionscope of the present invention. Any variation or replacement readilyfigured out by a person skilled in the art within the technical scopedisclosed in the present invention shall fall within the protectionscope of the present invention. Therefore, the protection scope of thepresent invention shall be subject to the protection scope of theclaims.

What is claimed is:
 1. A data transmission method, comprising:generating a preamble corresponding to a protocol version of atransmission on a wireless local area network, wherein the preamblecomprises a high efficiency signal (HE-SIG) field, wherein the HE-SIGfield comprises four symbols including a first orthogonal frequencydivision multiplexing (OFDM) symbol, a second OFDM symbol, a third OFDMsymbol and a fourth OFDM symbol, wherein the four symbols are arrangedin order, and input information bits of the first OFDM symbol are thesame as that of the second OFDM symbol, and wherein input informationbits of the third OFDM symbol are the same as that of the fourth OFDMsymbol, wherein the input information bits of the third and fourth OFDMsymbols include all left information bits except the input informationbits of the first and second OFDM symbols, in information bits that needto be carried in the HE-SIG field, wherein the generating the preamblecomprises processing the input information bits of the first and secondOFDM symbol, by using a channel encoder, an interleaver, and a firstmodulator, to obtain the first OFDM symbol, and, by using the channelencoder, without interleaving, and a second modulator to obtain thesecond OFDM symbol, wherein the first modulator and the second modulatorare same or different, and wherein the generating the preamble furthercomprises processing the input information bits of the third and fourthOFDM symbol, by using the channel encoder, the interleaver, and a thirdmodulator to obtain the third OFDM symbol, and, by using the channelencoder, without interleaving, and a fourth modulator to obtain thefourth OFDM symbol, wherein the third modulator and the fourth modulatorare the same or are different; and sending the preamble to a receive enddevice.
 2. The method according to claim 1, wherein a time domain signalof the first OFDM symbol is different from a time domain signal of thesecond OFDM symbol.
 3. The method according to claim 1, wherein thefirst modulator is a binary phase-shift keying (BPSK) modulator, and thesecond modulator is a quaternary binary phase shift keying (QBPSK)modulator.
 4. The method according to claim 1, wherein the thirdmodulator is a BPSK modulator.
 5. A data transmission method,comprising: receiving a preamble sent by a transmit end devicecorresponding to a protocol version of a transmission on a wirelesslocal area network, wherein the preamble comprises a high efficiencysignal (HE-SIG) field, wherein the HE-SIG field comprises four symbolsincluding a first orthogonal frequency division multiplexing (OFDM)symbol, a second OFDM symbol, a third OFDM symbol and a fourth OFDMsymbol, wherein the four symbols are arranged in order, and whereininput information bits of the second OFDM symbol are the same as that ofthe first OFDM symbol, and input information bits of the third OFDMsymbol are the same as that of the fourth OFDM symbol, wherein the inputinformation bits of the third and fourth OFDM symbols include allinformation bits, other than the input information bits of the first andsecond OFDM symbols, in information bits that need to be carried in theHE-SIG field; and processing the first OFDM symbol, the second OFDMsymbol, the third OFDM symbol and the fourth OFDM symbol in thepreamble, wherein the processing the first OFDM symbol, the second OFDMsymbol, the third OFDM symbol and the fourth OFDM symbol in the preamblecomprises parsing the first OFDM symbol to obtain the input informationbits of the first and second OFDM symbols, by using a channel decoder, ade-interleaver, and a first de-modulator, and parsing the second OFDMsymbol to obtain the input information bits of the first and second OFDMsymbols, by using the channel decoder without de-interleaving, andfurther by using a second de-modulator, wherein the first de-modulatorand the second de-modulator are the same or are different, and whereinthe processing the first OFDM symbol, the second OFDM symbol, the thirdOFDM symbol and the fourth OFDM symbol in the preamble further comprisesparsing the third OFDM symbol to obtain the input information bits ofthe third and fourth OFDM symbols, by using the channel decoder, thede-interleaver, and a third de-modulator, and parsing the fourth OFDMsymbol to obtain the input information bits of the third and fourth OFDMsymbols, by using the channel decoder without de-interleaving, andfurther by using a fourth de-modulator, wherein the third de-modulatorand the fourth de-modulator are the same or are different.
 6. The methodaccording to claim 5, wherein a time domain signal of the first OFDMsymbol is different from a time domain signal of the second OFDM symbol.7. The method according to claim 5, wherein the first de-modulator is abinary phase-shift keying (BPSK) de-modulator, the second de-modulatoris a quaternary binary phase shift keying (QBPSK) de-modulator.
 8. Themethod according to claim 5, wherein the third de-modulator is a BPSKde-modulator.
 9. A transmit end device, for transmitting a preamblecorresponding to a protocol version of a transmission on a wirelesslocal area network, comprising: a channel encoder; an interleaver; afirst modulator; a second modulator; a third modulator; a fourthmodulator; and a transmitter; wherein the preamble comprises a highefficiency signal (HE-SIG) field, the HE-SIG field comprises foursymbols including a first orthogonal frequency division multiplexing(OFDM) symbol, a second OFDM symbol, a third OFDM symbol and a fourthOFDM symbol, wherein the four symbols are arranged in order, and inputinformation bits of the first OFDM symbol are the same as that of thesecond OFDM symbol, and input information bits of the third OFDM symbolare the same as that of the fourth OFDM symbol; wherein the inputinformation bits of the third and fourth OFDM symbols include allinformation bits, other than the input information bits of the first andsecond OFDM symbols, in information bits that need to be carried in theHE-SIG field; wherein the input information bits of the first and secondOFDM symbol are processed by the channel encoder, the interleaver, andthe first modulator to obtain the first OFDM symbol; wherein the inputinformation bits of the first and second OFDM symbol are processed bythe channel encoder, without interleaving, and further by the secondmodulator to obtain the second OFDM symbol, wherein the first modulatorand the second modulator are the same or are different; wherein theinput information bits of the third and fourth OFDM symbol are processedby the channel encoder, the interleaver, and the third modulator toobtain the third OFDM symbol; wherein the input information bits of thethird and fourth OFDM symbol are processed by the channel encoder,without interleaving, and further by the fourth modulator to obtain thefourth OFDM symbol, wherein the third modulator and the fourth modulatorare same or different; and wherein the transmitter is configured to sendthe preamble to a receive end device.
 10. The device according to claim9, wherein a time domain signal of the first OFDM symbol is differentfrom a time domain signal of the second OFDM symbol.
 11. The deviceaccording to claim 9, wherein the first modulator is a binaryphase-shift keying (BPSK) modulator, the second modulator is aquaternary binary phase shift keying (QBPSK) modulator.
 12. The deviceaccording to claim 9, wherein the third modulator is a BPSK modulator.13. A receive end device, for receiving a preamble sent by a transmitend device corresponding to a protocol version of a transmission on awireless local area network, comprising: a channel decoder; ande-interleaver; a first de-modulator; a second de-modulator; a thirdde-modulator; and a fourth de-modulator; wherein the preamble comprisesa high efficiency signal (HE-SIG) field, the HE-SIG field comprises foursymbols including a first orthogonal frequency division multiplexing(OFDM) symbol, a second OFDM symbol, a third OFDM symbol and a fourthOFDM symbol, wherein the four symbols are arranged in order, and inputinformation bits of the second OFDM symbol are the same as that of thefirst OFDM symbol, and input information bits of the third OFDM symbolare the same as that of the fourth OFDM symbol; wherein the inputinformation bits of the third and fourth OFDM symbols include all leftinformation bits except the input information bits of the first andsecond OFDM symbols, in information bits that need to be carried in theHE-SIG field; wherein the first OFDM symbol is parsed to obtain theinput information bits of the first and second OFDM symbols, by thechannel decoder, the de-interleaver, and the first de-modulator; whereinthe second OFDM symbol is parsed to obtain the input information bits ofthe first and second OFDM symbols, by the channel decoder withoutde-interleaving, and further by a second de-modulator, wherein the firstde-modulator and the second de-modulator are the same or are different;and wherein the third OFDM symbol is parsed to obtain the inputinformation bits of the third and fourth OFDM symbols, by the channeldecoder, the de-interleaver, and the third de-modulator; and wherein thefourth OFDM symbol is parsed to obtain the input information bits of thethird and fourth OFDM symbols by the channel decoder, withoutde-interleaving, and further by the fourth de-modulator, wherein thethird de-modulator and the fourth de-modulator are the same or aredifferent.
 14. The device according to claim 13, wherein a time domainsignal of the first OFDM symbol is different from a time domain signalof the second OFDM symbol.
 15. The device according to claim 13, whereinthe first de-modulator is a binary phase shift keying (BPSK)de-modulator, the second de-modulator is a quaternary binary phase shiftkeying (QBPSK) de-modulator.
 16. The device according to claim 13,wherein the third de-modulator is a BPSK de-modulator.